In domain-learning theory, learning in a specific knowledge domain is postulated as a progressive process that is characterized by interactions of knowledge, interests, and learning strategies accrued during each of the acclimation, competency, and proficiency learning stages (Alexander, Jetton, & Kulikowich, 1995). The purpose of this study was to examine the interrelations among prior knowledge, individual and situational interest, and learning strategies and their interactive impact on learning in physical education. The Model of Domain Learning (MDL) was used as the theoretical framework to guide this research. Data were collected from 202 sixth-grade learners from three middle schools and consisted of their individual interest in softball, their knowledge and skill levels in softball, their rating of situational interest in their softball classes, and their self-reported learning strategy use during learning. Learners' physical engagement (recorded in total steps using Yamax Digiwalkers) were measured to represent learning process outcome. Learners' knowledge achievement and individual interest change were assessed using arithmetic difference between pretest and posttest scores of the measures. The data were analyzed using correlation and path modeling analysis. Findings suggest that the learners brought various prior knowledge and skill to the learning process with different individual interest in the content. The learners at the acclimation stage demonstrated fragmented and incoherent interrelations of knowledge, interests, and learning strategies, while those at the competency stage showed a coherent pattern of the interrelations. During learning, situational interest played a role as a primary motivator for the learners at the acclimation stage and facilitated the learners at the competency stage. Knowledge acquisition and individual interest development were found occurring simultaneously as a result of interactions among prior knowledge, individual interest, situational interest, and learning strategies. Results also indicate that situational interest was internalized into individual interest for the learners at the acclimation stage when they were acquiring new knowledge. The findings suggest that the MDL is tenable model to explain the effect of the interactive relationships among knowledge, interests, and learning strategies on learning in physical education.