This observation study documents the amount and quality of mathematics instruction provided to students with intellectual and developmental disabilities in kindergarten through second grade in self-contained special education settings. We observed six special education teachers and their students (N = 12) during a total of 967 min allotted to early numeracy and mathematics instruction. Mathematics and early numeracy instruction comprised 61.2% of all observed time allotted for mathematics, followed by non-instruction (32.7%), mathematics assessment (5.7%), and instruction in other areas (0.3%). Observed mathematics content included Numbers and Quantitative Reasoning, and Measurement. Mean ratings of student engagement and instructional quality across areas were medium and low-average, respectively. Although student engagement did not differ by who was leading instruction, instructional quality differed between teachers and paraeducators. Class sizes were small, and teachers most often taught students as a whole class or individually. Students used technology, manipulatives, and printed instructional materials during learning.