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 five 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. Multi-level 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). [This paper was published in the "Elementary School Journal" v119 n4 p651-676 2019 (EJ1217817).]