Teachers' instructional decisions, such as lesson goals, how students are grouped, or how students are recognized and evaluated, can affect their students' level of motivation related to physical activity. A physical educator's primary responsibility is to create a classroom environment that enhances motivation and fosters positive attitudes and behaviors regarding healthy lifestyle choices. This article describes the central role of the instructional situation (class climate) and how the structuring of this environment can influence the motivation processes of students. It discusses two types of motivation climates (mastery and performance) and how each impacts students' motivational and behavioral processes. It also provides strategies that teachers can use to design and implement a mastery climate in their class and discusses factors that influence student perceptions about the classroom climate. (Contains 2 tables and 1 figure.)