dissenting.
I respectfully dissent from the majority's determination that 'the settlement agreement between the parties obliged Jerry to pay non-educational child support to their youngest child, Stephanie, upon her attendance at an institution of higher learning. In my view, the terms of the agreement are unambiguous and should be interpreted to mean that when Stephanie went to college, Jerry became obliged to pay her education expenses, including room, board, tuition, books, and other incidental fees, but was not required to pay non-educational support unless a subsequent support order was entered. Further, in the event that any ambiguity does exist in the terms of the agreement, I believe that equity compels that it should be construed against Margaret to prevent a severe injustice.
As the majority observed, it is a longstanding rule that the non-custodial parent must make payments in the manner, amount, and at the times required by an in gross support order until a court orders modification or all of the children are emancipated or have reached the age of twenty-one. Thacker v. Thacker, 710 N.E.2d 942, 944 (Ind.Ct.App.1999). © This means that any modification of child support is legally invalid unless and until it is approved by the trial court. A corollary of this rule is that a trial court may not modify support awards retroactively, and modification of a support obligation may relate back, at the earliest, to the date a petition to modify was filed. Beehler v. Beehler, 693 N.E.2d 638, 641 (Ind.Ct.App.1998); see also Ind.Code § 31-16-16-6 {providing 'that a court may not retroactively modify an obligor's duty to pay a delinquent child support obligation).
One basis for modification of a support order is when the non-custodial parent assumes extraordinary education expenses in addition to the basic child support obligation. According to Ind. Child Support Guideline 3(E), any extraordinary education expense incurred on behalf of children may be added to the basic child support obligation. The commentary to this guideline provides that, if college expenses are provided separate from child support, support paid to the custodial parent should be reduced, at least while the student is away from the household and at school. See Child Supp. G. 6, emt. ("Extraordinary Educational Expenses"). In keeping with this guideline, we have held that when a parent is obligated to pay a portion of a child's college expenses in addition to child *651support, the trial court must consider full or partial abatement of a parent's basic child support obligation. In re Marriage of Tearman, 617 N.E.2d 974, 977 (Ind.Ct.App.1993). This avoids the duplication of payment for a single expense, resulting in a windfall to the custodial parent. Id.
In this instance, the majority concluded that in addition to the educational support that Jerry had already paid, he was also responsible for non-educational support ar-rearage in the amount of $43,900. Op. at 648. Notwithstanding Child Supp. G. 3(E) and the supporting commentary, the majority determined that Jerry was not entitled to any abatement of his non-educational child support. This is because he failed to file a petition for modification while Stephanie was still in college, and, therefore, any abatement would amount to an impermissible retroactive modification of his support obligation. Op. at 649-650.4
I must respectfully disagree with the majority's interpretation of the child support provision and construe it to provide that Jerry was not obligated to pay noneducational child support after Stephanie began college unless a subsequent support order was entered. The settlement agreement provides in relevant part:
The parties agree ... that custody be awarded to [Margaret], and [Jerry] be ordered to pay the sum of $231.00 per week for their [children's] support, being $115.50 per week, per child.... When either of the minor children are able and elect to attend a college, trade school or other post-secondary educational institution, [Jerry] shall pay the room, board, books, tuition and fees incidental to such education together with such support as the court may from time to time deem proper.
Appellant's App. p. 8. The dispute between the parties centers on the meaning of the clause "together with such support as the court may from time to time deem proper." Appellant's App. p. 8; Appellant's Br. p. 7-8; Appellee's Br. p. 6-9.
The majority construes this language "as permitting the court to further modify the then current amount of non-educational support" if such modification becomes appropriate. Op. at 648. Had this clause stated that Jerry was to pay the specified educational expenses "together with such support as the court has deemed proper," I would be inclined to accept the majority's interpretation. However, the language employed is permissive and focuses on future, not past, support orders by the trial court. Therefore, I interpret it as referring to future support orders that may be issued by the court upon application by one of the parties, not the continued payment of the existing non-educational support payment. Accordingly, I believe that Jerry acted according to the terms of the settlement agreement when, upon Stephanie's attendance at college, he began paying the specified educational expenses but ceased paying non-educational support. Thus, his action did not constitute an impermissible unilateral reduction in child support.
I also believe that Margaret's actions support Jerry's interpretation of the settlement agreement or, at the very least, dictate that any ambiguity in the contract should be construed against her. For four and one-half years Margaret never indicated that she interpreted the agreement to require both educational and non-educational support or that she considered *652Jerry in violation thereof. Appellant's App. p. 16, 19. Instead, she remained silent, permitting Jerry to unwittingly accumulate thousands of dollars in non-educational support arrearage, while at the same time faithfully outlaying large amounts of money for Stephanie's food, shelter, tuition, medical, and other financial needs while she was in college.5 Had Margaret made Jerry aware of her alternate interpretation of their agreement he could have sought a modification of the custody order and requested an appropriate credit on his non-educational child support obligation. See Child Supp. G. 3(B). Instead, Margaret waited until one and one-half years after Stephanie turned twenty-one to file her verified motion to show cause, by which time Jerry was precluded from receiving any credit by the rule barring retroactive modification of child support.
In my view, Jerry should not be faulted or penalized for failing to take action to resolve an ambiguity that he was not aware existed. See Moss v. Frazer, 614 N.E.2d 969, 971-72 (Ind.Ct.App.1998) (stating that "we cannot fault [the father] for not raising an ambiguity in the 1979 decree until he was made aware of [the mother's) alternate interpretation when she filed her contempt petition"). Nor should Margaret be allowed to receive a windfall as a result of such prejudicial and unscrupulous "gotcha" litigation tactics. See Wilson Fertilizer & Groin, Inc. v. ADM Mill. Co., 654 N.E.2d 848, 856 (Ind. Ct.App.1995). (Kirsch, J., concurring and dissenting) (disagreeing with the majority's application of the law to the facts enabling appellee-defendant to play and win "the latest version of 'Legal Gotcha'" and receive goods that it had ordered without paying for them) trans. denied; Salce-do v. Asociacion Cubana, 368 So.2d 1837, 18339 (Fla.Dist.Ct.App.1979) (condemning "gotcha" litigation tactics); Thomas v. City of Miami Beach, 753 So.2d 591, 591 (Fla. Dist.Ct.App.2000) (disapproving of "gotcha" administrative practices) trans. denied; see also In re Marriage of Tearman, 617 N.E.2d at 977 (observing that the purpose of permitting a credit against the non-custodial parent's basic support obligation for educational support costs is to avoid double payment of the same expense resulting in a windfall for the custodial parent). Thus, I believe that equity dictates that the agreement should be construed in Jerry's favor to prevent a severe injustice.6
*653At the same time, I acknowledge that child support is intended to provide for the support and maintenance of the parties' children, and that the amount of support due to Stephanie is considerably less under Jerry's interpretation of the agreement. Nevertheless, I perceive no injustice to Stephanie and no undue burden on Margaret in upholding the agreement according to Jerry's interpretation. Parties are free to draft their own settlement agreement upon dissolution of their marriage, and those agreements may provide for the payment of child support. See Niccum v. Niccum, 734 N.E.2d 637, 639 (Ind.Ct.App.2000). Onee such agreement is approved by the trial court and incorporated into the divorcee decree, it becomes legally binding and enforceable. See In re Marriage of Loeb, 614 N.E.2d 954, 957 (Ind.Ct.App.1993).
In this instance, the parties entered into an agreement that more than adequately provided for Stephanie's care and support. In accordance with what he believed to be the terms of that agreement, Jerry made regular non-educational child support payments until Stephanie turned eighteen and began attending college.7 Thereafter, Jerry paid for Stephanie's room, board, and tuition at two fine private colleges. He also paid for her books and supplies, medical insurance, spending money, and other incidental expenses, leaving Margaret to provide for Stephanie's care and support only during vacations and summer break. Appellant's App. p. 16, 17, 18, 19. The purpose of child support "is the welfare of the child and not the punishment of the father." Rohn v. Thuma, 408 N.E.2d 578, 582 (Ind.Ct.App.1980) (quoting Commonwealth v. Larsen, 211 Pa.Super. 30, 234 A.2d 18, 20 (1967)). It is apparent from the record that Stephanie was well provided for during her minority and will suffer no prejudice as a result of a ruling in her father's favor.
That being said, I also take issue with the rule that prevents Jerry from receiving a retroactive credit against his noneducational child support payments if the agreement is interpreted in Margaret's favor. He is not permitted to receive this credit because it constitutes a modification of the existing child support payment, and a bright-line rule exists that any modification must be pre-approved by the court. See Thacker, 710 N.E.2d at 944. This bright-line rule operates to prevent the custodial parent, as constructive trustee of the child's support, from contracting away the benefits of the trust. See Nill v. Mar*654tin, 686 N.E.2d 116, 118 (Ind.1997)8 It is apparently based on the premise that the custodial parent, usually the mother, is incapable of negotiating in the best interests of herself and her child and must be protected by the judicial system from the possible oppression and machinations of the non-custodial parent.9 Such premise is patronizing and unsupportable in light of the realities of today's society where it can no longer be presupposed that women are inadequate representatives of their own and their children's interests. Moreover, this rule against private ordering inappropriately undermines the role of the individual in our society and the constitutional right to contract. Where the justification for the rule has disappeared, so should the rule. Cf Martin, 686 N.E.2d at 118-19 (Boehm, J., dissenting) (arguing that the rationale for the rule requiring court pre-approval of child support modifications "disappears where both parents agree," and advocating for an exception to the rule where the custodial and non-custodial parents agree to a reduction in support after the death or emancipation of a child). For this reason, the rule should not be applied in this instance to prevent Jerry from receiving a retroactive credit against his noneducational support obligation.
In sum, I believe that Jerry's interpretation of the contract was proper and supported by the fact that Margaret failed to raise any ambiguity for four and one-half years. Accordingly, I would find that Jerry was acting pursuant to the terms of the settlement agreement when he ceased paying non-educational child support after Stephanie began attending college. Therefore, I vote to reverse the judgment of the trial court.
. The majority also determined, and I agree, that none of the narrow exceptions to the rule against retroactive modification of child support are applicable to this case. 649. See op. at
. The record does not indicate exactly how much Jerry paid in educational support expenses while Stephanie was in college. When Jerry attempted to testify regarding the amount of these expenditures, Margaret objected on the grounds of relevance, and that objection was sustained by the trial court. However, our independent research reveals that the current yearly cost for room, board, and tuition at Asbury College, Kentucky, which Stephanie attended for one year, is approximately $17,000. See Asbury College website at- http://www.asbury.edu/admis-sions/expenses/cost.cfm (last visited May 25, 2002). The yearly cost for room, board, and tuition at Anderson College, Indiana, which Stephanie attended for three years, is approximately $21,400. See Anderson College website at www.anderson.edu/finaid/costs/html (last visited May 25, 2002). These annual fees do not include books and supplies, spending money, transportation, and other incidental costs. They also do not take into account any grants or scholarships that Stephanie may have received to offset these expenses.
. Had Jerry affirmatively pleaded the defenses of laches or equitable estoppel I would have found in his favor on either of those bases. The equitable doctrine of laches precludes a plaintiff from asserting a claim where the defendant shows: (1) plaintiff's inexcusable delay in asserting rights; (2) plaintiff's implied waiver arising from knowing acquiescence in existing conditions, and (3) circumstances causing the defendant prejudice. Pickett v. Pickett, 470 N.E.2d 751, 754 (Ind.Ct.App.1984). The mere passage of time *653is insufficient to establish laches as there must be unreasonable delay and prejudice to the opposing party. Id. The defense of equitable estoppel is similar to the laches defense but contains the additional element of reliance by the defendant. Id. The elements of these defenses are satisfied inasmuch as Margaret remained inexcusably silent for four and one-half years, permitting Jerry to rely to his detriment upon her apparent acquiescence to his interpretation of the child support provisions of their settlement agreement. However, as Ind. Trial Rule 8(C) requires that the defenses of laches and equitable estoppel be affirmatively pled, and Jerry did not raise those defenses in his pleadings, we cannot reverse the trial court and uphold his interpretation of the contract on either of those bases. See Ind. Trial Rule 8 (providing in relevant part: "A responsive pleading shall set forth affirmatively and carry the burden of proving ... estoppel [and] laches").
. In fact, In April 1990 Jerry even agreed to an increase in his support payments from $231 a week to $280 a week (constituting . $140 per week per child). Appellant's App. p. 11. Further, notwithstanding the fact that Stephanie's older brother turned twenty-one in 1996, Jerry continued to pay $280 a week according to the in gross order until August 1999 when Stephanie turned twenty-one. Appellant's App. p. 7, 12, 13.
. Other cases where the courts have declined to enforce an agreement between parents modifying the child support obligation include: Thacker, 710 N.E.2d at 944; Ort v. Schage, 580 N.E.2d 335, 336 (Ind.Ct.App.1991); Kaplon v. Harris, 567 N.E.2d 1130, 1132 (Ind.1991); Pickett v. Pickett, 470 N.E.2d 751, 754 (Ind.Ct.App.1984); Haycraft v. Haycraft, 176 Ind.App. 211, 375 N.E.2d 252, 255 (1978); Grace v. Quigg, 150 Ind.App. 371, 276 N.E.2d 594, 601 (1971).
. Ironically, it has been my experience that judges often cast only a cursory glance over such agreements. Thus, a rule designed to protect the custodial parent and child simply serves to create greater expense for the parties and to ensure the employment of lawyers.