Petitioner-appellant Christopher Randall Ward appeals the trial court's denial of his petition to modify custody of his son, Sean. The original custody order had been entered in Georgia when his marriage to respondent-appellee Michelle Leann Ward was dissolved. Christopher raises four issues for our review which we consolidate and restate as: whether the trial court erred when it concluded Christopher failed to show a substantial and continuing change in the cireumstances of his son's custody.
FACTS
Christopher and Michelle married on June 5, 1982, in Georgia. During the course of their marriage, they had two sons, Joshua, now age eight, and Sean, now age four. When the couple decided to live apart in June 1988, they sent Sean to live with his maternal aunt and uncle, the MecDivitts, in Indiana. By March of 1989, Michelle had also moved into the MeDivitts' home, and both Michelle and Sean were living there when the Wards entered a separation and custody agreement on August 14, 1989. A Georgia court accepted the Wards' agreements, and on September 12, 1989, entered judgment dissolving the Wards' marriage.
Pursuant to the custody agreement, Christopher was given custody of their older son, Joshua, and Michelle was given custody of their younger son, Sean. The agreement also reflected Sean's living arrangement with the MecDivitts, and gave Michelle, as Sean's legal custodian, the right to determine his appropriate residence.1 When the custody agreement was entered, Michelle was also living with the McDivitts. Just days after the marriage dissolution was final, however, Michelle returned to Georgia to "try to get back on [her] feet[,|"' but she left Sean in Indiana with the MeDivitts. Record at 110. Except for a six-month period in 1990 when Michelle returned to Indiana, Michelle has continued to reside in Georgia while Sean has resided in Indiana. Michelle is hopeful, however, that she will soon be able to introduce Sean back into her Georgia home.
On March 28, 1990, Christopher filed a petition to modify custody in the Juvenile Court of Gwinnett County, Georgia, but on August 23, 1990, the Georgia court dismissed the petition for lack of jurisdiction. *169On December 18, 1991, Christopher petitioned the Fountain Circuit Court in Indiana to modify Sean's custody. After hearing evidence, the court denied Christopher's petition for modification. The court concluded Christopher failed to show a substantial change in circumstances (or any change in circumstances) sufficient to warrant modifying the custody order.
Christopher now appeals the denial.
DISCUSSION AND DECISION
Jurisdiction
We begin by noting this dispute encompasses modification of a custody order entered by a Georgia court. Because Sean was physically present in Indiana, and had been for over two years, the Georgia court declined jurisdiction to hear Christopher's modification petition. The Georgia court's dismissal was consistent with the policies of the Uniform Child Custody Jurisdiction Act, GA.CODE ANN. § 74-501, et seq., to
assure that litigation concerning the custody of a child takes place ordinarily in the state with which the child and his family have the closest connection and where significant evidence concerning his care, protection, training, and personal relationships is most readily available and to assure that the courts of [Georgia] decline the exercise of jurisdiction when the child and his family have a closer connection with another state.
GA.CODE ANN. § 74-502(a)(8). See also IND.CODE 81-1-11.6 et seq. Because the Georgia court declined to assume jurisdiction to modify a custody order it entered, and jurisdiction in the Circuit Court of Fountain County, Indiana, was otherwise proper, Indiana had jurisdiction to hear Christopher's petition to modify Sean's custody order. IND.CODE 31-1-11.6-14(a).
Standard of Review2
When reviewing the denial of a petition for modification, this court will reverse the judgment only if the trial court abused its discretion. Elbert v. Elbert (1991), Ind.App., 579 N.E.2d 102, 105. When making our determination, we will not reweigh the evidence, reassess witness credibility, or substitute our judgment for that of the trial court. Id. If the trial court's judgment is supported by any evidence or legitimate inferences drawn therefrom, we will not disturb it. Id. If, however, the trial court's decision is clearly against the logic and effect of the facts and circumstances before the court, reversal is appropriate. Id.
Modification of custody orders is governed by IND.CODE 81-1-11.5-22(d) which provides:
The court in determining said child custody, shall make a modification thereof only upon a showing of changed cireum-stances so substantial and continuing as to make the existing custody order unreasonable. In making this determination, the court shall not hear evidence on matters occurring prior to the last custody proceeding between the parties unless such matters relate to a change of circumstances.
As the above provision mandates, a custody order may be modified only upon satisfying the following two-prong test.3 First, the noncustodial parent must meet the strict burden of establishing the existence of a substantial and continuing change in the circumstances of the child's *170custody. Schenk v. Schenk (1991), Ind.App., 564 N.E.2d 973, 977. If the court concludes a sufficient change in circumstances exists, the court must then determine whether the changed circumstances are of such a decisive nature that the existing custody order is unreasonable and modification is necessary for the child's welfare. Id. The decisive change in circumstances must be either in the custodial home or in the child's treatment in the custodial home. Gerber v. Gerber (1985), Ind.App., 476 N.E.2d 531, 532. The potentially disruptive influence upon a child passed between parents necessitates the strict showing of unreasonableness. Moutaw v. Moutaw (1981), Ind.App., 420 N.E.2d 1294, 1296.
The Wards' Custody Agreement
Christopher seeks to modify Sean's custody order because Michelle has left Sean in Indiana while she lives in Georgia. Although he agreed Michelle would get custody of Sean, Christopher argues he did not agree Michelle and Sean could live apart.
The following provision in the parties' custody agreement is central to this dispute:
(1) Husband shall have custody of the older minor child of the parties, JOSHUA WAYNE WARD. Wife shall have custody of the minor child of the parties, CHRISTOPHER SEAN WARD. It is acknowledged by the parties in making this Agreement that the minor child, CHRISTOPHER SEAN WARD, is presently physically residing with his maternal aunt and uncle where and through whom he has been able to receive necessary and extraordinary medical and dental services. Husband acknowledges that the child's residence with his maternal aunt and uncle may be continuing for an unspecified period of time and that wife, as legal custodian of said child, shall determine the appropriate residence of said child.
Record at 31.
After hearing testimony from both Christopher and Michelle, the trial court denied Christopher's petition for modification for failure to demonstrate a substantial and continuing change in the circumstances of Sean's custody. The trial court concluded Sean's living arrangement with the McDi-vitts was exactly the same as it was when the custody order was entered. Specifically, the court made the following comments:
[The language [in the custody agreement] is clear.... Language couldn't be any clearer than that.... These folks determined what the best interest of the children were [sic] in 1989.... The circumstances are exactly the same today as they were when this agreement was signed in 1989. ... [I]f I were sitting as the judge in Georgia I'm not sure I would have approved an agreement like this, but the judge in Georgia seemed to think it was the best thing and certainly the parents thought it was the best thing.
Record at 185-87.
We disagree with the trial court's assessment of the facts and interpretation of the Wards' custody agreement. The record reveals Michelle was living with Sean at the McDivitts' home when the Wards entered the custody agreement and when the Georgia court accepted it on September 12, 1989. Less than one month after the dissolution decree was entered, Michelle moved to Georgia but left Sean in Indiana. Except for a six-month period in 1990 when Michelle returned to Indiana, Michelle has continued to reside in Georgia while Sean resides in Indiana. It simply is not true, therefore, that "[the circumstances are exactly the same today as they were when this agreement was signed in 1989." Record at 186. Michelle and Sean no longer live in the same home; indeed, they do not live in the same state.
Furthermore, it is ambiguous, at best, whether the Wards' custody agreement permits Sean to remain with the MeDivitts while Michelle lives permanently in Georgia. Christopher testified at the modification hearing that he understood the custody agreement required Michelle "either to stay with Sean in Indiana or ... to bring Sean back to Georgia with her if she chose to move back to Georgia." Record at 58. *171Michelle testified that she believed the agreement permitted her to determine the appropriate residence for Sean, and she had determined that that residence was with the MeDivitts. Record at 107.
Pursuant to Michelle's interpretation, Christopher is bound by Michelle's decision concerning the best home for Sean regardless of whether she and Sean share the same home or whether Michelle exercises any responsibility for Sean's upbringing. When the Wards signed the custody agreement, we do not believe Christopher intended to relinquish the right to challenge the living arrangements Michelle chooses, especially when those arrangements involve Michelle living three states away from Sean. Furthermore, we find no evidence Christo, pher intended to give up the right to chal lenge Michelle's complete lack of responsibility for their child's upbringing. These, we believe, are the challenges Christopher makes today.
Conclusion
Under the facts before us, the trial court erred when it concluded Christopher failed to show a substantial and continuing change in the cireumstances of Sean's custody. Christopher satisfied the first prong of IND.CODE 31-1-11.5-22(d) when he showed Michelle moved to Georgia in the fall of 1989 while Sean has remained in Indiana. The trial court never reached the second prong of IND.CODE 31-1-11.5-22(d), however: whether the changed circumstances are of such a decisive and continuing nature that the existing custody order is unreasonable and modification is necessary for Sean's welfare. See Schenk, supra, at 977. This determination is properly for the trial court.
We reverse the denial of Christopher's petition for custody modification, and remand for proceedings consistent with this opinion.
ROBERTSON, J., concurs. MILLER, J., dissents with separate opinion.. The McDivitts stipulated at the hearing that they have no legal claim or right to custody of Sean.
. The record reveals Michelle moved for dismissal after Christopher, the petitioner, presented his evidence. Technically, Michelle's motion was an Ind. Trial Rule 41(B) motion for involuntary dismissal with prejudice. In reality, however, a full-blown hearing had been conducted, and both Christopher and Michelle were afforded the opportunity to testify. Choosing substance over form, we will review the trial court's ruling as a denial of Christopher's petition for modification rather than as a dismissal with prejudice. See Benefit Trust Life Ins. Co. v. Waggoner (1985), Ind.App., 473 N.E.2d 646.
. Notwithstanding Christopher's extensive argument to the contrary, we agree with the trial court that this is not a custody dispute between a natural parent and a third party. Rather, it is a dispute about the interpretation and modification of an existing custody order. The standard of proof applicable to a custody dispute between a natural parent and a third party enunciated in Hendrickson v. Binkley (1974), 161 Ind.App. 388, 316 N.E.2d 376, cert. denied, 423 U.S. 868, 96 S.Ct. 131, 46 LEd.2d 98, simply does not apply.