We examined the relationship among key instructional process variables and the achievement of students with and without disabilities as measured by both interim and end-of-year summative assessments. Examination of the instructional process data indicated that students with and without disabilities receiving mathematics instruction in the same classrooms had virtually equal opportunities to learn (OTL), yet there were significant differences in these two groups of students' mathematics achievement on both interim and summative tests. Subsequent regression analyses indicated that the collection of five OTL scores, along with Grade Level and Special Education status, accounted for 44% of the variance in student's end-of-year mathematics scores. Discussion of these results focuses on equality and equity of opportunity to learn and the role these processes may play in interim and endof-year achievement gaps between students with and without disabilities.