The purpose of this dissertation was to investigate the effects of different pairings of students by language dominance on achievement in mathematics. The effects of self-paced materials written in English, Spanish, and in both languages was also sought. Participants in the study were students in two schools in a bilingual program in Bayamon, Puerto Rico. Three methods to ascertain an individual student's language dominance were employed: 1)an English Idiom test, 2)English and Spanish Reading Comprehension Tests, and 3)oral conversations between students and their English and Spanish teachers. The students were paired with either a member of their own dominance group or a member of the other dominance group where dominance was determined using three criteria. Results indicated that the English dominant students paired with Spanish dominant students achieved significantly better on the post-test than did the English dominant students paired with English dominant students. The Spanish dominant students paired with English dominant students achieved significantly better on the post-test than did Spanish dominant students paired with Spanish dominant students. The bilingual materials had no significant effect upon achievement in any of the paired groups. (Author/AM)