We examined associations between the quality of kindergarten teachers' mathematics instruction and their students' achievement and motivation in mathematics. Using a sample of 20 kindergarten teachers and their 285 students, we rated 5 video-recorded mathematics lessons per teacher throughout the spring semester with the Mathematical Quality of Instruction (MQI). We collected information about students' achievement from teacher ratings of student performance relative to state standards and an individually administered standardized measure of mathematical reasoning. We obtained data about students' mathematics motivation (self-competence beliefs, interest, effort expenditure, and need for support) through individual interviews with the children and via teacher ratings. Multilevel modeling analyses indicated that scores on the MQI's "ambitious mathematics instruction" scale and the "whole lesson" scale predicted students' end-of-year progress on kindergarten mathematics standards but not their standardized test scores. The whole lesson scores were associated with teacher-rated students' motivation for mathematics (interest and need for support).