We describe and validate a novel, scalable, group-based assessment of executive functions (EFs) in a classroom setting using tablet computers. Relative to the conventional method of a more controlled, one-on-one individual assessment (IA), the group assessment (GA) can be administered quickly to many students, requires less training for assessors, and measures performance in a naturalistic classroom setting. In a socioeconomically and ethnically diverse sample of 269 students in third through fifth grade, we show that IA and GA scores for the same tasks were highly inter-correlated, equally reliable, and showed analogous associations with known EF covariates. IA and GA scores independently predicted teacher-rated self-regulated classroom behavior and standardized test scores. Further, only the GA score emerged as a unique predictor of academic achievement when controlling for prior achievement. We are sharing the tablet apps, source code, and supporting materials for this GA procedure at no cost under an open-source license.