Facts: Mother and Father, who were never married, are the parents of Child. They initially shared equal parenting time on a rotating two-week schedule.

A March 2023 interim order established Father’s paternity, noted Mother’s safety concerns, required Father’s parenting time to be supervised, prohibited contact between the parents, and directed them to mediation. Their June 2023 mediated agreement continued equal parenting time and provided that the parents would reach a further agreement, or return to mediation, before Child entered school.

In October 2024, the trial court entered a permanent parenting plan awarding each parent 182.5 days but naming neither as the primary residential parent.

When Child reached school age, Father petitioned to change custody, explaining that the parents lived roughly four hours apart and could no longer maintain a rotating schedule.

The trial court agreed that Child’s reaching school age was a material change in circumstances. After a best-interest analysis, it named Father the primary residential parent, directed that Child attend school where Father lived, and reduced Mother’s time to every third weekend, rotating holidays, and alternating summers. Although the ordered schedule gave Mother far fewer days, the parenting plan and the resulting child-support calculation continued to credit both parents with 182.5 days.

At the modification hearing, Mother repeatedly tried to introduce evidence that Father had abused Mother’s daughter from a previous relationship. Mother testified that, when the parties mediated, the allegation had been reported, but her daughter had not yet been forensically interviewed, Mother did not yet know the details, and the Department of Children’s Services had not yet substantiated the allegation.

Father objected that the allegation and later substantiation predated the October 2024 order and were barred by res judicata, and the trial court sustained the objections.

The trial court found both parents fit and treated the alleged abuse as moot and res judicata. It also found inapplicable the best-interest factor addressing abuse and the factor addressing prior restrictions on parenting time. Thus, the trial court completed its best-interest analysis without allowing Mother to develop the record on the alleged abuse.

Mother appealed.

On Appeal: The Court of Appeals vacated the trial court’s ruling.

In Tennessee, a request to change the primary residential parent requires two distinct inquiries. The petitioner must first prove a material change in circumstances by a preponderance of the evidence, and only then does the court determine whether modification is in the child’s best interest.

Although a final custody decision is res judicata as to facts existing or reasonably foreseeable when the decision was made, that principle did not render the alleged abuse evidence irrelevant to the separate best-interest inquiry after the parties agreed that Child reaching school age constituted a material change.

The evidence was particularly relevant to factor 8, each parent’s fitness as it relates to parenting; factor 11, abuse of the child, the other parent, or any other person, including Child’s siblings; and factor 15, prior reductions or restrictions in custody or parenting time and the reasons for them.

The Court of Appeals held that the substance and purpose of Mother’s excluded evidence were apparent from the context, res judicata did not bar its consideration in the best-interest analysis, and its exclusion more probably than not affected substantial rights:

From the foregoing testimony, the substance of the evidence excluded in this case and the reasons for admission could not be more apparent. Father’s own attorney stated, “there’s a letter substantiating [Father] for sex abuse, that’s all it says.”

Further, the testimony excerpts above make clear that the trial court agreed with Father’s argument that the alleged abuse was not relevant to whether there had been a material change in circumstance. As a result, the trial court found that “any alleged misconduct was both moot and res judicata as the alleged misconduct occurred prior to [Mother] entering into the agreed parenting plan outlined in the parties’ mediation agreement dated June 5, 2023 and encompassed in the order and parenting plan signed by the court on October 8, 2024.” However, the trial court’s analysis disregards the fact that, throughout these proceedings, Mother has maintained that the evidence of alleged abuse is relevant to the trial court’s best interest analysis — an analysis distinct from determination of whether there has been a material change of circumstance.

The evidence was relevant even though the alleged conduct concerned another child. Factor 11 expressly reaches abuse of “any other person,” including Child’s siblings, while factor 8 addresses parental fitness. Factor 15 also applied because the March 2023 interim order restricted Father to supervised parenting time after noting Mother’s safety concerns.

The Court further explained:

As to the excluded evidence of Father’s alleged abuse, whether Father perpetrated abuse on another child is significant and relevant to this Child’s best interest. In finding, as to statutory factors 8 and 11, that this evidence was barred as “moot and res judicata,” the trial court abused its discretion by incorrectly identifying and failing to properly apply the appropriate legal principles. Specifically, we conclude that the trial court’s decision to deny evidence of Father’s alleged abuse of another child, “substantially impaired the trial court’s ability to make an informed custody decision based on the best interest of th[is] [C]hild.” Accordingly, . . . “excluding such evidence more probably than not affected the substantial rights of the parties and the child, whose best interest is at the heart of the inquiry.”

Vacating the custody order also required vacating child support. The Court noted that the worksheet used 182.5 days for each parent even though the schedule awarded Mother substantially less parenting time. On remand, the trial court must use the parents’ actual residential days or, if it deviates from the Child Support Guidelines, make the findings required by Tenn. Comp. R. & Regs. 1240-02-04-.07.

K.O.’s Comment: (1) Custody modification has two steps, and lawyers should identify which step each item of proof addresses. Res judicata may prevent a party from relying on old facts to establish the threshold material change, but that does not automatically make those facts irrelevant to Child’s best interest after a material change is established. Here, Child reaching school age supplied the material change. The alleged abuse concerned the different question of which parenting arrangement served Child’s best interest.

(2) The safest practice is still to make an offer of proof. Mother survived the absence of one because the questions, objections, testimony, and statements of counsel made the substance and relevance of the excluded evidence unmistakable. Lawyers should not assume that an appellate court can always reconstruct excluded proof from context. When evidence is excluded, tell the trial court what the evidence would show and why it is admissible.

Source: Lucas v. Fifield (Tennessee Court of Appeals, Eastern Section, August 20, 2026).

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