This study investigated the role of school-related variables in explaining academic proficiency (AP) performance in Hebrew (L2) and English (L3) among immigrant youth. The following sets of variables were examined: (1) school background (2) academic, linguistic and social-psychological support, and (3) professional staff and school resources allocated for immigrant students. The sample included 267 Russian (L1) speaking students drawn from 18 Israeli high schools. Students' AP level was assessed via AP tests in L2 and L3. Data about the schools were collected through interviews with the school principals. Multivariate analysis of covariance, controlling for socioeconomic status (SES), arrival age and gender indicated that students' performance significantly varied as a function of the school-related variables although the effect of these variables on students' AP scores in L2 and L3 was not to the same extent. The variables educational track (comprehensive schools), upper SES, social-psychological support, teacher training, parental involvement, and provision of an immigrants' class were associated with higher grades in the respective languages whereas provision of academic and linguistic support were related to lower scores. These results highlight the role of the particular learning environment and context as a source of variation in L2 and L3 performance.