We examine whether parental and school investments reinforce or compensate for student performance. Our analysis exploits school-starting-age rules in 34 countries, capturing achievement variation that arises because younger children typically underperform their older peers. Parents respond to lower performance by providing additional homework help, while schools allocate weaker students to smaller classes and offer more remedial tutoring. Notably, parents provide more support to low-performing children in nearly all countries studied. Compensatory investments increase over grade levels, suggesting parents and schools respond as information about achievement is revealed. Moreover, our evidence suggests that parental and school investments are substitutes.