Make-believe play has been theorized to promote self-regulation skills and other positive child outcomes. In this study, we examine the make-believe play approach featured in the "Tools of the Mind" (Tools) early childhood curriculum, which identifies students' self-regulation cultivation among its core programmatic aims. Using data from 42 classrooms in the United States, we specified latent growth models to investigate the association between Tools make-believe play and children's self-regulation development throughout pre-kindergarten, kindergarten, and first grade (N = 646 students aged between four and seven years old). We found that higher implementation frequency and fidelity of Tools play predicted less self-regulation growth. Implications for policy and practice are discussed.