This mixed-method study examined the implementation and the challenges to implementation for participants in randomized controlled trials of two school-based programs for early adolescents: the Tier One Word Generation (WG) program, and the Tier Two Strategic Adolescent Reading Intervention (STARI). Levels of implementation for WG and STARI varied substantially across teachers and classrooms, with mean levels of 40% for fourth- and fifth-grade WG, 31% for sixth- and seventh-grade WG, and 47% for STARI. The three most common implementation challenges for WG were lack of time, multiple new programs/curricula happening at the same time, and time lost to testing and test prep. The three most common implementation challenges for STARI were student misbehavior, student absences, and time lost to testing and test prep. In order to succeed, efforts to find programs that work and to improve educational outcomes must address these formidable problems in U.S. public schools.