The relation between mathematical achievement in early childhood and future academic success is well established. However, our knowledge about the effect of instruction on mathematical performance is often reliant upon self-report or videotaped instruction measures and standardized achievement assessments. The current study uses teacher audio recordings to examine the role of classroom mathematics instruction in the growth of adaptive early mathematical skills. Kindergarten children (N = 98, M(age) = 5.55 years, 53% male) were followed across the school year. Findings suggested children with the lowest levels of adaptive mathematics skills grew the most across the school year, suggesting that basic skills continue to be the focus in early elementary years. Further, no aspects of mathematics instruction predicted growth in children's addition or counting skills. These results highlight the need for more robust and ecologically valid measurement in assessing classroom mathematics instruction in future research.