This study documents differences between pre- and in-service content area teachers' beliefs about: whether English language learners (ELLs) should be included in content area classes, the kind of instructional support (IS) they should receive, and responsibility for ELLs' language and academic achievement. Questionnaire data were collected from 94 in-service and 101 pre-service content area teachers. Although several significant differences were found in pre- and in-service and female and male teachers' beliefs about responsibility for ELLs' language and academic development, both service and gender groups appeared to hold similar beliefs about ELLs' inclusion in mainstream classes. Results also revealed that some beliefs held by female teachers about IS for ELLs significantly differed from those of males'; however, the effects of service and gender on certain beliefs may be contingent upon a number of background factors. The article concludes with pedagogical implications for teacher education for classrooms with linguistically and culturally diverse learners. (Contains 4 tables.)