Responding to the declining trend in reading motivation in and beyond the elementary school years, the authors aimed to enhance late-elementary school students' autonomous reading motivation. Toward this end, the authors evaluated the influence of a teacher professional development grounded in self-determination theory on fifth-grade students' (n = 664) autonomous motivation for in-school and leisure-time reading. A quasi-experimental repeated measures design was set up with experimental and control conditions. The experimental condition consisted of teachers participating in a professional development workshop aimed at providing the knowledge and skills necessary to implement an autonomy-supportive and structuring teaching style, whereas the control condition included teachers who continued with their current teaching repertoire. Multilevel piece-wise growth analyses corroborated that students in the experimental group reported increased recreational autonomous reading motivation from pretest to posttest relative to the control group. Additional analyses made clear that boys in particular benefitted from their teachers' professional development.