The performance of students from different racial or ethnic subgroups and of students receiving bilingual (Spanish and English) or monolingual (English only) instruction in mathematics was studied using students from schools in the QUASAR (Qualitative Understanding Amplifying Student Achievement and Reasoning) project, a mathematics education reform project supporting innovative instruction for middle school students in economically disadvantaged communities. Patterns of ethnic distribution vary across QUASAR sites, and linguistic diversity was found at many QUASAR sites. Data were from administration of the QUASAR Cognitive Assessment Instrument (QCAI) to approximately 1,000 students in grades 6, 7, and 8 at 2 QUASAR project schools, one of which provided bilingual classes for its predominantly Latino population. Results indicate that the instructional programs of both schools provided similar educational opportunities in mathematics, with parallel gains for African American and Caucasian students. Results also indicate that high quality mathematics instruction can be made available to students in bilingual classes. Evidence also supports the validity of the QCAI. (Contains 5 figures and 40 references.) (SLD)