This study examines the October 1991 exit-level Texas Assessment of Academic Skills (TAAS) mathematics results of 18,290 11th-grade Hispanic Americans, African Americans, and White non-Hispanic Americans from Texas urban districts. Substantial differences existed in the passing rates of the three ethnic groups. The passing rate for White non-Hispanics was 79 percent; for Hispanics, 48 percent; and for African Americans, 40 percent. To explore the differences in passing rates, the researcher controlled for mathematics course placement and semester grade, which reduced, but did not eliminate the gaps among ethnic groups. Across all cells, the median difference in passing rates between Hispanics and White non-Hispanics was 18; between African Americans and White non-Hispanics it was 25.5. When another control, passing or failing the exit-level TAAS reading test, was added, the gap was further reduced, but not eliminated. Hispanic and White non-Hispanic passing rates still differed by 11.5, and those for African American and White non-Hispanics differed by 19.5. Various explanations are discussed for the persistence of these gaps, including differential preparation of ethnic groups in the same course and cultural bias in the TAAS. Fourteen tables present study findings. (Contains 20 references.) (SLD)