This study aimed to evaluate the effectiveness of an early intervention based on the Quinn Project on motor and cognitive performance in preschool children with developmental delays. The research employed an experimental design with pretest, posttest, and follow-up phases. The statistical population included all children with developmental delays in Tehran in 2021-2022 academic year. A convenience sample was obtained by screening at kindergartens and preschool centers using the Denver‑II developmental screening test, yielding 30 children who were randomly assigned to experimental and control groups. Research instruments included the Denver-II screening test, Bruininks-Oseretsky Test of Motor Proficiency, and the Wechsler Preschool and Primary Scale of Intelligence-Third Edition (WPPSI-III). Data were analyzed using split-plot ANOVA. Results showed significant differences between the experimental and control groups in fine motor skills, gross motor skills, and cognitive performance (p < 0.001). Additionally, the main effect of time was significant for all three variables, with notable improvements from pretest to posttest. These findings suggest that early intervention based on the Quinn Project effectively enhances motor and cognitive functioning in preschool children with developmental delays.