This paper provides a theoretical overview of the late pretest issue and empirically assesses the bias-precision tradeoff in the experimental evaluation of the efficacy of adding a curriculum designed to support the development of children's self-regulation skills (Scaffolded Self-Regulation, SSR) to an established early mathematics curriculum (Building Blocks, BB) to form a synthesized curriculum,
BBSSR. The RCT described in this paper is conducted in three large districts in Southern California.