High-quality caregiving, that is emotionally responsive and cognitively stimulating, in the first 5 years of life is linked to STEM achievement and school success at age 15, and this relation is facilitated through increased STEM achievement in Grades 3–5. Further, this link is particularly strong for children from low-income families who benefit uniquely from exposure to high-quality early childcare and education. This work informs policy conversation around investing in high-quality early childcare and education for children from underserved communities. (author abstract)