Our appellants were plaintiffs in a civil action in the District Court against the District of Columbia. At the close of their case the trial judge directed a verdict for the defendant-appellee. This verdict was on alternative grounds. Relying on the test established in Elgin1 the judge held that the evidence adduced showed that the alleged negligent act was “a clearly discretionary matter” that had been determined by the school authorities and, therefore, suit against the District of Columbia was barred by governmental immunity. Alternatively the judge held that the plaintiffs failed to present adequate evidence upon which a jury “could reasonably determine that the allocation of the available teachers was a negligent act.” We affirm on the latter, alternate ground and do not reach the other contention.
The facts are very simple. On the day of the alleged negligent act, Ronald T. Butler, the minor appellant, was a seventh grade student at the Woodson Junior High School. En route to his printing class, following lunch, he encountered a classmate who warned him that the boys already in the classroom intended to scare him as he entered. He was no more than three steps inside the classroom when an object that “was pointed and * * * sharp and * * * felt like a piece of metal” struck him in the left eye, causing pain and resulting in permanent loss of sight in the eye. It was shown that small metallic type was a part of the equipment used in the classroom, and one witness testified that he noticed a few pieces of such type lying on the floor in the general area where Ronald had fallen.
A teacher from another classroom came into the printing class and, apparently not realizing the seriousness of the injury, nudged Ronald with his foot and told him to get up. Several minutes later (no more than ten and possibly as few as five), Mr. Weir, the printing class teacher, came into the room. Ronald was taken to the nurse’s office, his parents were summoned, and in due course he was taken to D. C. General Hospital for treatment.
Dr. John O’Neill, a pediatric ophthalmologist, the only expert witness called by the plaintiffs, testified that, although neither he nor the other doctors who treated Ronald could determine what the object was that had caused the damage, generally speaking the sharper the object the less force was required to cause such an injury.
The plaintiffs’ case rested on their contention that the school authorities were negligent in their supervision of this classroom and that this negligence was the proximate cause of Ronald’s injury.2 This argument rested on two bits of evidence: (1) that the printing teacher was not physically present to supervise the students when the class convened and (2) testimony tending to show that both Mr. Weir and the principal had prior knowledge that “horse*1152play” and throwing occurred in this classroom when the teacher was not present.3
The evidence showed that the teacher was not present at the start of this particular class, because he had been assigned to duty as a hall or cafeteria supervisor. Under a plan established by the principal, who was the general supervisor of internal school functions, each teacher had been designated duties during the lunch period. This plan was designed to place teachers in positions where supervision was most needed. There were some twelve hundred students in the school, and, in an effort to provide for maximum safety and order, the teachers were deployed in various places outside their own classrooms during certain periods when the students generally were outside the classrooms. One of these periods was the lunch break.
Plaintiffs offered no evidence that Mr. Weir was not performing his assigned duty on the day in question but, to carry their burden of showing negligence on this point,4 rely on the fact that the teacher was not present in the classroom. In essence they contend that it was negligent for the school authorities not to have a teacher assigned to a particular classroom containing fourteen pupils while this same teacher, in the exercise of the principal’s discretion, was supervising part of an area that may have contained a thousand pupils.
Appellants stress the trial judge’s assumption that “there had been complaints of previous horseplay by students in the absence of the classroom teacher.”5 This factor does not support the argument based upon it. It is common knowledge susceptible of judicial notice that small boys may indulge in horseplay — shoot a paperclip, snap a rubber-band, or throw a pencil — when a teacher is tardy' or turns his or her back.6 The possibility of such an occurrence had been anticipated by the school authorities here involved. Knowing that if a teacher was assigned cafeteria duty, or that if, in patrol of a corridor not near his own classroom during the lunch break, he might not be physically present in that classroom at the start of the following class period, various rules had been established. The principal had given the students instructions on the first day of school that were designed to govern their conduct in the absence of a teacher. These were buttressed by fourteen specific rules established by Mr. Weir to apply specifically to the conduct of his printing class students. These were printed and distributed to each class member. They directed the students, upon entering the room in the absence of the teacher, to sit down, work on their projects, not throw type, and await further instructions.7 Thus, faced with the knowledge that children, and especially thirteen-year-old boys, will *1153throw at, kick, hit or push a fellow pupil if a teacher is not immediately present, and using the available supervisory personnel, the authorities balanced the need for a teacher to supervise several hundred students milling about the corridors and the cafeteria against the need to supervise fourteen students in a certain classroom for a short period of time.
The problem is not unlike that relating to other governmental operations involving the safety or well-being of numbers of people; such are streets, sidewalks, sewers, snow removal, playgrounds, and many others. The problem of negligence under such conditions is discussed at some length in Booth,8 Urow,9 Elgin,10 and similar cases.11 We need not repeat. In the case now before us the plaintiffs do not say there was no plan, or that the plan was defective, or that the plan was not being followed. They say simply that the teacher was absent from the classroom at the critical moment in this affair, and they say that was negligence. Liability for negligence is not established by such allegations or evidenee4
Affirmed.
. Elgin v. District of Columbia, 119 U.S.App.D.C. 116, 337 F.2d 152 (1964).
. Plaintiffs-appellants also make two evi-dentiary arguments on appeal. The first concerns the trial court’s refusal to allow Ronald to give testimony as to what Mr. Weir said or did as he entered the room. On objection from defense counsel the evidence was excluded as irrelevant. The second of these objections relates to the trial court’s refusal to allow a fellow student to testify as to student behavior in the classroom on prior occasions when the teacher was absent. This was ex-eluded when the witness was unable to approximate the dates or times when these prior acts occurred.
As to the latter of these arguments we find no prejudice, since for purposes of the directed verdict the trial judge assumed prior knowledge on the part of the officials-defendan ts. And as to the first contention we find this ruling to be within the ambit of the trial judge’s discretion as to admissibility of evidence. See Post, et al. v. United States, 132 U.S.App.D.C. 189, 193-194, 407 F.2d 319, 323-324 (1968).
. Now, for the first time, on appeal appellant makes reference to the teacher’s failure- to lock up these dangerous metallic pieces of type as further evidence of negligence. This theory, or the alternative theory that the students should not have been allowed in the room in the absence of their teacher were not raised at trial. No evidence appears on any ' theory except the teacher’s failure to be present when class convened.
. The plaintiffs did not call Mr. Weir. No explanation for this is present in the papers before us. Nor was any attempt made to show that Mr. Weir was unnecessarily late for his class.
. This assumption was based on testimony by Ronald’s father, who, along with his wife, visited the principal of the school on the day following the injury to their son. The elder Butler testified that the principal told them that he had had complaints of students throwing type while Mr. Weir was not present in the room. This was denied by the principal at trial.
. Oilman v. Board of Education, 300 N.Y. 306, 90 N.E.2d 474 (1949), rehearing denied, 301 N.Y. 662, 93 N.E.2d 927 (1950); Lawes v. Board of Education of City of New York, 16 N.Y.2d 302, 266 N.Y.S.2d 364, 213 N.E.2d 667 (1965); Carrol v. Fitzsimmons, 153 Colo. 1, 384 P.2d 81 (1963); cf. Annot., 86 A.L.R. 2d 489, 565 (1962).
. Diamond v. Board of Education of City of New York, 12 Misc.2d 47, 171 N.Y.S.2d 703 (1958).
. Booth v. District of Columbia, 100 U.S.App.D.C. 32, 241 F.2d 437 (1956).
. Urow v. District of Columbia, 114 U.S.App.D.C. 350, 316 F.2d 351 (1963).
. Supra note 1.
. Amelchanko v. Borough of Freehold, 42 N.J. 541, 201 A.2d 726 (1964); Huff v. Northampton County Board of Education, 259 N.C. 75, 130 S.E.2d 26 (1963).