Many public and private initiatives have focused on improving prekindergarten (PK) through Grade 12 mathematics education, given that the mathematics content learned before college is foundational for later learning and college success across STEM subjects. Although decades of educational research have studied PK-12 mathematics interventions, the field lacks a comprehensive understanding of which interventions work, for whom, and under what conditions. This meta-analytic project aimed to examine the heterogeneity in mathematics intervention effects by synthesizing 25 years of randomized experiments of interventions designed to improve mathematics achievement. It describes intersections of interventions, intervention components, and outcomes that appear especially promising for future intervention research. [SREE documents are structured abstracts of SREE conference symposium, panel, and paper or poster submissions.]