This study investigates teachers' pedagogical content knowledge, professional beliefs, work-related motivation, and self-regulation as aspects of their professional competence. Specifically, it examines how these aspects impact instruction and, in turn, student outcomes. In a nationally representative sample of 194 German secondary school mathematics classes, multiple measures were used to assess teacher competence, instructional quality, and students' achievement and motivation. The effect of teachers' professional competence on student outcomes was estimated in a 1-year repeated-measures design. Two-level structural equation models revealed positive effects of teachers' pedagogical content knowledge, enthusiasm for teaching, and self-regulatory skills on instructional quality, which in turn affected student outcomes. In contrast, teachers' general academic ability did not affect their instruction. The multidimensional model of teachers' professional competence introduced in this article seems suited to stimulate further research on the personal indicators of teacher quality.