This study established interrater reliability and preliminary developmental score guidelines for preschool children (ages 3–5 yr) on the Motor Planning Maze Assessment (MPMA). We administered the MPMA to 80 typically developing preschoolers and found age effects for Time, Error, and Total scores for each of three mazes. Five-year-olds obtained lower (better) scores than 4-yr-olds, who scored lower than 3-yr-olds. Older children completed the mazes with significantly fewer errors in significantly less time than younger children. Interrater reliability was excellent on the total MPMA score (intraclass correlation coefficient = 0.96) and individual maze scores (0.90–0.98). Results of this study provide evidence that the MPMA can serve as a reliable, objective screening of a preschooler’s ability to plan and execute motor movements. A larger reference population is needed to increase generalizability.