This study examined the effect of Connecting Math Concepts Level K on basic math skills of typically-developing preschoolers and preschoolers with developmental delays. Results indicate that children had improved performance from pretest to posttest; effect sizes on the Battelle Developmental Inventory (BDI) Cognitive Domain were generally educationally significant (d > 0.25) for both groups of students. (Copyright © 2011, National Institute for Direct Instruction (NIFDI). All rights reserved).