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 minutes allotted to early numeracy and mathematics instruction. Mathematics and early numeracy instruction comprised 59.7% of all observed time allotted for mathematics, followed by non-instruction (32.7%), mathematics assessment (7.3%), and instruction in other areas (0.3%). Observed content included Numbers and Quantitative Reasoning, and Measurement. Student engagement and instructional quality ratings were highest during activities involving counting non-moveable objects, and did not differ by who was leading instruction. 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.