delivered the opinion of the Court.
This is an appeal from a three-judge District Court for the District of Maryland. Nine minors, appellees here, .brought an action under 42 U. S. C. § 1983, seeking a declaratory judgment and injunctive relief to prevent the State from filing exceptions with the Juvenile Court to proposed findings and recommendations made by masters of that court. The minors’ claim was based on an alleged violation of the Double Jeopardy Clause of the Fifth Amendment, as applied to the States through the Fourteenth Amendment. The District Court’s jurisdiction was invoked under 28 U. S. C. §§ 1343, 2281, and 2284 (as then written); this Court’s jurisdiction, under 28 U. S. C. § 1253.
I
In order to understand the present Maryland scheme for the use of masters in juvenile court proceedings, it is necessary to trace briefly the history both of antecedent schemes and of this and related litigation.
Prior to July 1975, the use of masters in Maryland juvenile proceedings was governed by Rule 908 (e), Maryland Rules of Procedure. It provided that a master “shall hear such cases as may be assigned to him by the court.” The Rule further directed that, at the conclusion of the hearing, the master transmit the case file and his “findings and recommendations” to the Juvenile Court. If no party filed exceptions to these findings and recommendations, they were to be “promptly . . . confirmed, modified or remanded by the judge.” If, however, a party filed exceptions — and in delinquency hearings, only the State had the authority to do so — then, after notice, the Juvenile Court judge would “hear the entire matter or such specific matters as set forth in the exceptions de novo.”1
*207In the city of Baltimore, after the State filed a petition alleging that a minor had committed a delinquent act,2 the clerk of the Juvenile Court3 generally would assign the case to one of seven masters.4 In the ensuing unrecorded hearing, the State would call its witnesses and present its evidence in accordance with the rules of evidence applicable in criminal cases. The minor could offer evidence in defense. At the conclusion of the presentation of evidence, the master usually would announce his findings and contemplated recommendations. In a minority of those cases where the recommendations favored the minor’s position, the State would file exceptions, whereupon the Juvenile Court judge would try the case de novo.5
In 1972, a Baltimore City Master concluded, after a hearing, that the State had failed to show beyond a reasonable doubt that a minor, William Anderson, had assaulted and robbed a woman. His recommendation to the Juvenile Court judge reflected that conclusion. The State filed exceptions. Anderson responded with a motion to dismiss the notice of exceptions, contending that Rule 908 (e), with its provision for a de novo hearing, violated the Double Jeopardy Clause. The Juvenile Court judge ruled that juvenile proceedings as such were not outside the scope of the Double Jeopardy Clause. *208He then held that the proceeding before him on the State’s exceptions would violate Anderson’s right not to be twice put in jeopardy and, on that basis, granted the motion to dismiss. The judge granted the same relief to similarly situated minors, including several who later initiated the present litigation.
The State appealed and the Court of Special Appeals reversed. In re Anderson, 20 Md. App. 31, 315 A. 2d 540 (1974). That court assumed, for purposes of its decision, that jeopardy attached at the commencement of the initial hearing before the master. It held, however:
“ [T]here is no adjudication by reason of the master’s findings and recommendations. The proceedings before the master and his findings and recommendations are simply the first phase of the hearing which continues with the consideration by the juvenile judge. Whether the juvenile judge, in the absence of exceptions, accepts the master’s findings or recommendatipns, modifies them or remands them, or whether, when exceptions are filed, he hears the matter himself de novo, there is merely a continuance of the hearing and the initial jeopardy. In other words, the hearing, and the jeopardy thereto attaching, terminate only upon a valid adjudication by the juvenile judge, not upon the findings and recommendations of the master.” Id., at 47, 315 A. 2d, at 549 (footnotes omitted; emphasis added).
On this basis, the court concluded that the de novo hearing was not a second exposure to jeopardy.
On appeal by the minors, the Court of Appeals affirmed, although on a rationale different from that of the intermediate appellate court. In re Anderson, 272 Md. 85, 321 A. 2d 516 (1974). It held that “a hearing before a master is not such a hearing as places a juvenile in jeopardy.” Central to this holding was the court’s conclusion that masters in Maryland serve only as ministerial assistants to judges; although author*209ized to hear evidence, report findings, and make recommendations to the judge, masters are entrusted with none of the judicial power of the State, including the sine qua non of judicial office — the power to enter a binding judgment.6
In November 1974, five months after the Court of Appeals’ decision, nine juveniles sought federal habeas corpus relief, contending that by taking exceptions to masters’ recommendations favorable to them the State was violating their rights under the Double Jeopardy Clause. These same nine minors also initiated a class action under 42 U. S. C. § 1983 in which they sought a declaratory judgment and injunctive relief against the future operation of Rule 908 (e). The sole constitutional basis for their complaint was, again, the Double Jeopardy Clause. A three-judge court was convened to hear this matter, and it is the judgment of that court we now review.
Before either the three-judge District Court or the single judge reviewing the habeas corpus petitions could act, the-Maryland Legislature.,enacted legislation which, for the first time, provided a statutory basis for the use of masters in juvenile court proceedings. In doing so, it modified slightly the scheme previously operative under Rule 908 (e). The new legislation required that hearings before a master be recorded and that, at their conclusion, the master submit to the Juvenile Court judge written findings of fact, conclusions of law, and recommendations. Either party was authorized to file exceptions and could elect a hearing on the record or a de novo hearing before the judge. The legislature specified that the master’s “proposals and recommendations . . . for juvenile causes do not constitute orders or final action of the court.” Accordingly, the judge could, even in the absence of exceptions, reject a'master’s recommendations and conduct a de *210novo hearing or, if the parties agreed, a hearing on the record. Md. Cts. & Jud. Proc. Code Ann. § 3-813 (Supp. 1977).
In June 1975, within two months of the enactment of § 3-813 and before its July 1, 1975, effective date, the single-judge United States District Court held that the Rule 908 (e) provision for a de novo hearing on the State’s exceptions violated the Double Jeopardy Clause. Aldridge v. Dean, 395 F. Supp. 1161 (Md. 1975). In that court’s view, a juvenile was placed in jeopardy as soon as the State offered evidence in the hearing before a master. The court also concluded that to subject a juvenile to a de novo hearing before the Juvenile Court judge was to place him in jeopardy a second time. Accordingly, it granted habeas corpus relief to the six petitioners already subjected by the State to a de novo hearing. The petitions of the remaining three, who had not yet been brought before the Juvenile Court judge, were dismissed without prejudice as being premature.
In response to both the enactment of § 3-813 and the decision in Aldridge v. Dean, supra, the Maryland Court of Appeals, in the exercise of its rulemaking power, promulgated a new rule, and the one currently in force, Rule 911, to govern the use of masters in juvenile proceedings.7 Rule 911 differs from the statute in significant aspects. First, in order to emphasize the nonfinal nature of a master’s conclusions, it stresses that all of his “findings, conclusions, recommendations or . . . orders” are only proposed. Second, the State no longer has power to secure a de novo hearing before the Juvenile Court judge after unfavorable proposals by the master. The State still may file exceptions, but the judge can act on them only on the basis of the record made before the master and “such additional [relevant] evidence ... to which the *211parties raise no objection.” 8 The judge retains his power to accept, reject, or modify the master’s proposals, to remand to the master for further hearings, and to supplement the record for his own review with additional evidence to which the parties do not object9
*212Thus, Rule 911 is a direct product of the desire of the State to continue using masters to meet the heavy burden of juvenile court caseloads while at the same time assuring that their use not violate the constitutional guarantee against double jeopardy. To this end, the Rule permits the presentation and recording of evidence in the absence of the only officer authorized by the state constitution, see In re Anderson, 272 Md., at 104-105, 321 A. 2d, at 526-527, and by statute, § 3-813, to serve as the factfinder and judge.
After the effective date of Rule 911, July 1, 1975, the plaintiffs in the § 1983 action amended their complaint to bring Rule 911 within its scope. They continued to challenge the state procedure, however, only on the basis of the Double Jeopardy Clause. Other juveniles intervened as the ongoing work of the juvenile court brought them within the definition of the proposed class. Their complaints in intervention likewise rested only on the Double Jeopardy Clause.
The three-judge District Court certified the proposed class under Fed. Rule Civ. Proc. 23 (b) (2) to consist of all juveniles involved in proceedings where the State had filed exceptions to a master’s proposed findings of nondelinquency. That court then held that a juvenile subjected to a hearing before a master is placed in jeopardy, even though the master has no power to enter a final order. It also held that the *213Juvenile Court judge’s review of the record constitutes a “second proceeding at which [the juvenile] must once again marshal whatever resources he can against the State’s and at which the State is given a second opportunity to obtain a conviction.” 436 F. Supp. 1361, 1369 (Md. 1977). Accordingly, the three-judge District Court enjoined the defendant state officials10 from taking exceptions to either a master’s proposed finding of nondelinquency or his proposed disposition.
We noted probable jurisdiction solely to determine whether the Double Jeopardy Clause prohibits state officials, acting in accordance with Rule 911, from taking exceptions to a master’s proposed findings.11 434 U. S. 963 (1977).
*214II
The general principles governing this case are well established.
“A State may not put a defendant in jeopardy twice for the same offense. Benton v. Maryland, 395 U. S. 784. The constitutional protection against double jeopardy unequivocally prohibits a second trial following an acquittal. The public interest in the finality of criminal judgments is so strong that an acquitted defendant may not be retried even though The acquittal was based upon an egregiously erroneous foundation.’ ... If the innocence of the accused has been confirmed by a final judgment, the Constitution conclusively presumes that a second trial would be unfair.
“Because jeopardy attaches before the judgment becomes final, the constitutional protection also embraces *215the defendant’s Valued right to have his trial completed by a particular tribunal.’ . . . Consequently, as a general rule, the prosecutor is entitled to one, and only one, opportunity to require an accused to stand trial.” Arizona v. Washington, 434 U. S. 497, 503-505 (1978) (footnotes omitted).
In the application of these general principles, the narrow question here12 is whether the State in filing exceptions to a master’s proposals, pursuant to Rule 911,13 thereby “require [s] an accused to stand trial” a second time. We hold that it does not. Maryland has created a system with Rule 911 in which an accused juvenile is subjected to a single proceeding which begins with a master’s hearing and culminates with an adjudication by a judge.
Importantly, a Rule 911 proceeding does not impinge on the purposes of the Double Jeopardy Clause. A central purpose “of the prohibition against successive trials” is to bar “the *216prosecution [from] another opportunity to supply evidence which it failed to muster in the first proceeding.” Burks v. United States, 437 17. S. 1, 11 (1978). A Rule 911 proceeding does not provide the prosecution that forbidden “second crack.” The State presents its evidence once before the master. The record is then closed, and additional evidence can be received by the Juvenile Court judge only with the consent of the minor.
The Double Jeopardy Clause also precludes the prosecutor from “enhanc[ing] the risk that an innocent defendant may be convicted,” Arizona v. Washington, supra, at 504, by taking the question of guilt to a series of persons or groups empowered to make binding determinations. Appellees contend that in its operation Rule 911 gives the State the chance to persuade two such factfinders: first the master, then the Juvenile Court judge. In support of this contention they point to evidence that juveniles and their parents sometimes consider the master “the judge” and his recommendations “the verdict.” Within the limits of jury trial rights, see McKeiver v. Pennsylvania, 403 U. S. 528 (1971), and other constitutional constraints, it is for the State, not the parties, to designate and empower the factfinder and adjudicator. And here Maryland has conferred those roles only on the Juvenile Court judge. Thus, regardless of which party is initially favored by the master’s proposals, and regardless of the presence or absence of exceptions, the judge is empowered to accept, modify, or reject those proposals.14
Finally, there is nothing in the record to indicate that the procedure authorized under Rule 911 unfairly subjects the defendant to the embarrassment, expense, and ordeal of a second trial proscribed in Green v. United States, 355 U. S. *217184 (1957). Indeed, there is nothing to indicate that the juvenile is even brought before the judge while he conducts the “hearing on the record,” or that the juvenile’s attorney appears at the “hearing” and presents oral argument or written briefs. But even if there were such participation or appearance, the burdens are more akin to those resulting from a judge’s permissible request for post-trial briefing or argument following a bench trial than to the “expense” of a full-blown second trial contemplated by the Court in Green.
In their effort to characterize a Rule 911 proceeding as two trials for double jeopardy purposes, appellees rely on two decisions of this Court, Breed v. Jones, 421 U. S. 519 (1975), and United States v. Jenkins, 420 U. S. 358 (1975).15
In Breed, we held that a juvenile was placed twice in jeopardy when, after an adjudicatory hearing in Juvenile Court on a charge of delinquent conduct, he was transferred to adult criminal court, tried, and convicted for the same conduct. All parties conceded that jeopardy attached at the second pro*218ceeding in criminal court. The State contended, however, that jeopardy did not attach in the Juvenile Court proceeding, although that proceeding could have culminated in a deprivation of the juvenile’s liberty. We rejected this contention and also the contention that somehow jeopardy “continued” from the first to the second trial. Breed is therefore inapplicable to the Maryland scheme, where juveniles are subjected to only one proceeding, or “trial.”
Appellees also stress this language from Jenkins:
“[I]t is enough for purposes of the Double Jeopardy Clause . . . that further proceedings of some sort, devoted to the resolution of factual issues going to the elements of the offense charged, would have been required upon reversal and remand. Even if the District Court were to receive no additional evidence, it would still be necessary for it to make supplemental findings .... [To do so] would violate the Double Jeopardy Clause.” 420 TJ. S., at 370 (emphasis added).
Although we doubt that the Court’s decision in a case can be correctly identified by reference to three isolated sentences, any language in Jenkins must now be read in light of our subsequent decision in United States v. Scott, 437 U. S. 82 (1978). In Scott we held that it is not all proceedings requiring the making of supplemental findings that are barred by the Double Jeopardy Clause, but only those that follow a previous trial ending in an acquittal; in a conviction either not reversed on appeal or reversed because of insufficient evidence, see Burks v. United States, supra; or in a mistrial ruling not prompted by “manifest necessity,” see Arizona v. Washington, 434 U. S. 497 (1978). A Juvenile Court judge’s decision terminating a Rule 911 proceeding follows none of those occurrences. Furthermore, Jenkins involved appellate review of the final judgment of a trial court fully empowered to enter that judgment. Nothing comparable occurs in a Rule 911 proceeding. See n. 15, supra.
*219To the extent the Juvenile Court judge makes supplemental findings in a manner permitted by Rule 911 — either sua sponte, in response to the State’s exceptions, or in response to the juvenile’s exceptions, and either on the record or on a record supplemented by evidence to which the parties raise no objection — he does so without violating the constraints of the Double Jeopardy Clause.
Accordingly, we reverse and remand for further proceedings consistent with this opinion.
It is so ordered.
Rule 908 (e) was the sole authority for the use of masters in juvenile causes. The practice was not treated in Maryland statutes.
Maryland, like 39 other States, defines a delinquent act as one that, if committed by an adult, would violate a criminal statute. See statutes collected at McCarthy, Delinquency Dispositions Under the Juvenile Justice Standards: The Consequences of a Change of Rationale, 52 N. Y. U. L. Rev. 1093 n. 2 (1977).
The official name of the court is Circuit Court of Baltimore City, Division for Juvenile Causes.
In 1974, of 5,345 delinquency hearings conducted in the Juvenile Court, 5,098 were held before masters. The remaining 247 were assigned in the first instance to the judge.
In 1974, the Juvenile Court judge conducted 80 de novo, or “exceptions,” hearings in delinquency matters. All hearings before the judge were recorded.
When the minors appealed here from this decision, we dismissed for want of a substantial federal question, Epps v. Maryland, 419 U. S. 809 (1974), and also denied certiorari, Anderson v. Maryland, 421 U. S. 1000 (1975).
At the time of its promulgation, the new Rule was numbered 910. As a result of recent nonsubstantive amendments and recodification, it received the 911 designation, by which it is referred to throughout this opinion.
The juvenile, after filing exceptions, can still elect either a de novo hearing or a hearing on the record.
Rule 911, in its entirety, provides:
“a. Authority.
“1. Detention or Shelter Care.
“A master is authorized to order detention or shelter care in accordance with Rule 912 (Detention or Shelter Care) subject to an immediate review by a judge if requested by any party.
“2. Other Matters.
“A master is authorized to hear any cases and matters assigned to him by the court, except a hearing on a waiver petition. The findings, conclusions and recommendations of a master do not constitute orders or final action of the court.
“b. Report to the Court.
“Within ten days following the conclusion of a disposition hearing by a master, he shall transmit to the judge the entire file in the ease, together with a written report of his proposed findings of fact, conclusions of law, recommendations and proposed orders with respect to adjudication and disposition. A copy of his report and proposed order shall be served upon each party as provided by Rule 306 (Service of Pleadings and Other Papers).
“c. Review by Court if Exceptions Filed.
“Any party may file exceptions to the master’s proposed findings, conclusions, recommendations or proposed orders. Exceptions shall be in writing, filed with the clerk within five days after the master’s report is served upon the party, and shall specify those items to which the party excepts, and whether the hearing is to be de novo or on the record. A copy shall be served upon all other parties pursuant to Rule 306 (Service of Pleadings and Other Papers).
“Upon the filing of exceptions, a prompt hearing shall be scheduled on the exceptions. An excepting party other than the State may elect a hearing de novo or a hearing oil the record. If the State is the excepting party, the hearing shall be on the record, supplemented by such additional evidence as the judge considers relevant and to which the parties raise *212no objection. In either case the hearing shall be limited to those matters to which exceptions have been taken.
“d. Review by Court in Absence of Exceptions.
“In the absence of timely and proper exceptions, the master's proposed findings of fact, conclusions of law and recommendations may be adopted by the court and the proposed or other appropriate orders may be entered based on them. The court may remand the case to the master for further hearings, or may, on its own motion, schedule and conduct a further hearing supplemented by such additional evidence as the court considers relevant and to which the parties raise no objection. Action by the court under this section shall be taken within two days after the expiration of the time for filing exceptions.”
Defendants, appellants here, are the State’s Attorney for Baltimore City, the operations chief of the State’s Attorney’s Office for Baltimore City, the Chief State Attorney assigned to the Baltimore City Juvenile Court, and the Clerk of that court.
The State did not contend, either in the District Court or here, that appellees’ suit for injunctive relief should be dismissed under the abstention doctrine of Younger v Harris, 401 U. S. 37 (1971). In these circumstances, we are not inclined to examine the application of the doctrine sua sponte. See Ohio Bureau of Employment Services v. Hodory, 431 U. S. 471, 477-480 (1977) (“If the State voluntarily chooses to submit to a federal forum, principles of comity do not demand that the federal court force the case back into the State’s own system”).
There is also a mootness question in this case. At the time of final argument before the District Court, Fields, the last in a series of intervening plaintiffs, was the only named plaintiff with a live controversy against the State. By that time, the State had either withdrawn its exceptions against the other named plaintiffs or completed the adjudicatory process by securing a ruling, one way or the other, from the Juvenile Court judge. After final argument, but before the District Court announced its decision, the State withdrew its exceptions to the master’s proposals respecting Fields. Nevertheless, the District Court, at the outset of its decision, granted Fields’ motion to intervene and certified the class. 436 F. Supp., at 1362.
We conclude that under the principles announced in Sosna v. Iowa, 419 U. S. 393 (1975), the State’s action, with respect to the original named *214plaintiffs and the intervenors, did not deprive the District Court of the power to certify the class action when it did and that, accordingly, a live controversy presently exists between the unnamed class members and the State. In Sosna, we observed:
“[T]here may be cases in which the controversy involving the named plaintiffs is such that it becomes moot as to them before the district court can reasonably be expected to rule on a certification motion. In such instances, whether the certification can be said to ‘relate back’ to the filing of the complaint may depend upon the circumstances of the particular case and especially the reality of the claim that otherwise the issue would evade review.” Id., at 402 n. 11.
Here the rapidity of judicial review of exceptions to masters’ proposals creates mootness questions with' respect to named plaintiffs, and even perhaps with respect to a series of intervening plaintiffs appearing thereafter, “before the district court can reasonably be expected to rule on a certification motion.” Ibid.
In cases such as this one where mootness problems are likely to arise, district courts should heed strictly the requirement of Fed. Rule Civ. Proc. 23 (c)(1) that “[a]s soon as practicable after the commencement of an action brought as a class action, the court shall determine by order whether it is to be so maintained.” (Emphasis added.)
The State contends that jeopardy does not attach at the hearing before the master. Our decision in Breed v. Jones, 421 U. S. 519 (1975), however, suggests the contrary conclusion. “We believe it is simply too late in the day to conclude . . . that a juvenile is not put in jeopardy at a proceeding whose object is to determine whether he has committed acts that violate a criminal law and whose potential consequences include both the stigma inherent in such a determination and the deprivation of liberty for many years.” Id., at 529. The California juvenile proceeding reviewed in Breed involved the use of a referee, or master, and was not materially different — for purposes of analysis of attachment of jeopardy— from a Rule 911 proceeding. See generally In re Edgar M., 14 Cal. 3d 727, 537 P. 2d 406 (1975); cf. Jesse W. v. Superior Court, 20 Cal. 3d 893, 576 P. 2d 963 (1978).
It is not essential to decision in this ease, however, to fix the precise time when jeopardy attaches.
The District Court noted that Rule 911 differs from § 3-813, see supra, at 210-211, but concluded that under Maryland decisional law the Rule governs. 436 F. Supp., at 1365. The parties do not dispute the District Court’s reading of state law. Accordingly, like the District Court, we consider only Rule 911 in resolving the constitutional challenge.
It is not usual in a criminal proceeding for the evidence to be presented and recorded in the absence of the one authorized to determine guilt. But if there are any objections to such a system, they do not arise from the guarantees of the Double Jeopardy Clause.
Appellees also rely on Keener v. United States, 195 U. S. 100 (1904). There a Manila lawyer was charged with embezzling the funds of his client. He was tried before the judge of a “court of first instance” and acquitted. The United States took an appeal to the Philippine Supreme Court, which, after reviewing the record, entered a judgment of guilty and imposed sentence. This Court held that an Act of Congress, which extended double jeopardy guarantees to the Philippines, required reversal of the conviction.
The differences between the present case and Keener are material. There the trial judge was authorized to try serious criminal cases and to enter judgment, either of acquittal or conviction. The Philippine trial judge did not serve as an “assistant” or master of the Philippine Supreme Court for the purpose of making proposed findings to the appellate judges. Id., at 115, 121, 133. Mr. Justice Brown in dissent accurately characterized the Philippine trial judge’s role as embracing “the great and dangerous power of finally acquitting the most notorious criminals.” Id., at 137. The Philippine Supreme Court’s role was appellate, and its jurisdiction was invoked by the Government’s decision to appeal an otherwise binding judgment.
See also Trono v. United States, 199 U. S. 521 (1905). *221its rales relating to the use of masters, see ante, at 209-210, the record before us indicates that the character of the hearing has not materially changed since that decision.