Professional learning strategies often rely on the belief that teaching and learning outcomes are best when teachers have a clear understanding of students' thinking. This may seem like common sense -- after all, students are active participants in the learning process, so their thinking impacts the outcome. But does research support the assumption that teachers' knowledge of students' thinking matters? Researchers Heather C. Hill and Mark Chin address this issue in a study, "Connections between teachers' knowledge of students, instruction, and achievement outcomes," recently published in the "American Educational Research Journal." The study's findings have important implications for professional learning directors, coaches, and school leaders as these professionals consider how to incorporate students' development and learning needs into strategies to make the most of curriculum and materials.