This study explored bilingual school psychologists' assessment practices with students identified as English language learners (ELL). One thousand bilingual National Association of School Psychologist members were recruited nationwide, and 276 participated. Among those conducting language proficiency assessments of ELLs, many (58%) use comprehensive methods across four domains of language use. Participants generally use multifaceted assessment approaches and most (84.1%) assess acculturation as part of the assessment battery. Although few use interpreters, those who did reported a mix of best practices and discouraged practices in their use. Multiple regression results showed that engaging in continuing education activities about assessing ELLs predicted “best practices” when assessing language proficiency, selecting and using measures with ELLs with whom they share a second language, and using interpreters. A relationship was also found between engaging in applied preservice training with bilingual supervision and best practice behaviors assessing student acculturation. © 2010 Wiley Periodicals, Inc.