Getting Ready for School (GRS) is a new school readiness intervention for teachers and parents, designedto help children develop early literacy, math, and self-regulation skills. GRS was implemented in 19 HeadStart classrooms. In the present study we examined variability in different aspects of intervention fidelityincluding dosage, adherence, and child engagement. In addition, we studied the association among class-room, teacher and student characteristics and fidelity, and whether measures of fidelity were associatedwith children’s growth in math, early literacy, and self-regulation skills across the preschool year. Find-ings indicate that on average teachers reported completing almost 80% of the activities assigned, andthat they were observed to adhere fairly well to the lessons. Child engagement was observed to be mod-erate to high across classrooms. Classroom quality, as measured by the CLASS, and age of children werepositively associated with adherence. Teachers that had participated in GRS for two years were morelikely to complete more activities. Different components of fidelity were associated with child outcomes.Percentage completion of math and literacy activities were positively associated with growth in mathand literacy skills. Children in classrooms in which teachers adhered more faithfully to the curriculummade significantly greater gains in literacy, math, and self-regulation skills. Child engagement was pos-itively associated with a measure of executive function. Results highlight the importance of examiningimplementation fidelity. Implications for preschool teachers are discussed.