A binational team of investigators culturally adapted, implemented, and tested the efficacy in Mexico of "keepin' it REAL," a US-designed prevention intervention for youth. This article reports on the social validity of the adapted intervention by assessing its feasibility, acceptability, and utility, as perceived by participating middle school students, teachers/implementers, and school administrators. Middle schools (N = 36) were randomly assigned to (1) the culturally adapted version for Mexico ("Mantente REAL"), (2) the original intervention from the USA ("keepin' it REAL") translated into Spanish, or (3) a control condition (treatment as usual). Adult and child feedback about the adapted and original versions of the intervention indicate that both are feasible to implement in the Mexican context. Implementation fidelity was equally high for both versions of the manualized intervention. Students, however, were more satisfied with the culturally adapted version than with the non-adapted version. They reported gaining more knowledge, finding it more acceptable, applicable, and authentic, and they reported discussing the program with their family and friends more often. The findings support the feasibility of engaging classroom teachers to implement manualized prevention programs in Mexico. These findings also advance prevention science by documenting the importance of cultural adaptation as a means to increase students' identification with and acceptability of efficacious school-based interventions. The article discusses the practice, policy, and future prevention research implications of the findings for Mexico and their potential generalizability to other middle- and lower-income countries.