Schooling, socioeconomic status (SES), and genetics all play large roles in intelligence differences. However, it is unclear to what extent their contributions are unique and if they interact. Here we used a multitrait polygenic score for cognition (cog-PGS) with a quasi-experimental regression discontinuity design to isolate how months of schooling relate to intelligence in 7,853 children (aged 9-11). We found large, independent effects of schooling, cog-PGS, and SES on working memory, crystallized (cIQ), and fluid intelligence (fIQ). Intriguingly, we found evidence for gene-by-environment interplay between cog-PGS and SES for cIQ, and a trend in the same direction for fIQ. This interaction was negative meaning that the intelligence of the highest SES children was the least affected by genetic differences, while the lowest SES children were most affected by genetic variability. Schooling showed no interaction with cog-PGS or SES for the three intelligence domains tested. While schooling had strong main effects on intelligence, it did not lessen, nor widen the impact of these preexisting SES or genetic factors.