This study examined the mathematics achievement of grade three English-speaking pupils enrolled in French immersion or in an English program as a function of language of instruction and the extent to which their teachers used a locally developed mathematics curriculum document. The sample consisted of eight English program classes and four French immersion classes. French and English versions of an objectives-based mathematics test were administered in October, 1981, and equivalent forms plus a nonverbal aptitude test were given to the same pupils in May, 1982. All participating teachers completed a teacher survey. The English program pupils made significantly greater mathematics gains than their French immersion peers, although the latter had higher initial average scores. Regardless of program, pupils whose teachers reported greater use of the new curriculum document made more mathematics progress than did pupils whose teachers reported less use of the document. The combined effects of program and teacher variables affected mathematics achievement of the grade three pupils as predicted. (Author)