Teacher-rated classroom engagement and student self-reported motivation for mathematics were used to predict mathematics scores in 3rd and 5th grade. Students were grouped based on a combination of biological sex and SES quintiles resulting in 10 independent groups. The mathematics achievement patterns were predicted based upon a combined within-group model. Results indicated female mathematics achievement was not significantly related to self-reported mathematics motivation but was related to classroom engagement. In males, mathematics motivation was not significantly related to achievement for lowest SES males; however, there was a significant relationship for highest quintile class males. Conversely, classroom engagement was significant for lower class males and was not significantly related for highest quintile SES males. Implications of the results are discussed.