We used triannual reading curriculum-based measurement of oral reading fluency data from 11,834 U.S. students in Grades 2 and 3 enrolled in an evidence-based Tier 2 reading intervention program (Reading Corps) to investigate the extent to which family involvement in the intervention might buffer against a negative effect of lower intervention dosage. The relation between family involvement in Reading Corps and growth in oral reading fluency was stronger when students spent fewer hours in tutoring, suggesting that family involvement in tiered reading intervention can compensate for receiving less intervention dosage. There was noticeable variation in this effect across tutors, suggestive of tutor-level heterogeneity of this relation. The relation between sending family engagement materials to families and the materials that are returned to tutors also substantially varied across tutors. We discuss findings in terms practical significance for school-based academic intervention systems. We highlight limitations and opportunities for future directions as well.