This article reports on a large-scale study investigating the overall perception of multilingualism in the family environment of children enrolled in an English immersion program in primary schools across Spain and the potential relationship between these attitudes and the student’s academic performance. One thousand and one families participated in the study, based on a tailored questionnaire that evaluated three main aspects: (1) parents’ and guardians’ ratings of their children’s language skills; (2) language practices in the home, especially with respect to time allocated to different languages and multilingual practices such as code-switching; and (3) attitudes and general perception of the benefits and drawbacks of multilingualism in socio-economic, cultural, cognitive and professional terms. The complex results from this questionnaire, in addition to providing a more accurate picture of the family environment of students enrolled in these programs, show some significant correlations with academic performance, which we discuss here, with some reference to their educational implications.