This paper evaluates the contribution of external background factors which pertain to the child's environment (e.g., parent education, parent occupation, family size, etc.), and internal ones which reflect the child's time related experience with language (e.g., chronological age, age of L2 onset, etc.) to the development of linguistic skills in the two languages of bilingual children. 65 Russian-German (Mean age: 66mo, Range: 47-86mo) and 78 Russian-Israeli migrant children (Mean age: 70mo, Range: 58-81) with comparable mean length of L2 exposure (M=37mo) and family size (1.88 children) but different Socio-Economic Status (SES), were tested with a battery of language and their parents were interviewed.. Overall, internal, temporal, factors showed a stronger relationship to language measures than external, environmental, factors: age of L2 onset and length of L2 exposure correlated with L2, while parents' education/occupation showed positive correlations with both L1 and L2 measures. In the Russian-German cohort, which had a sub-group with relatively lower SES, SES positively correlated with L1 success as well.