Student engagement is an important contributor to school success, yet high school students routinely describe themselves as disengaged. Identifying factors that alter (increase) engagement is a key aspect of improving support for student achievement. This study investigated students' perceptions of autonomy, teacher connection, and academic competence as predictors of changes in student engagement within the classroom from the start to the end of a course. Participants were 578 (58% female) diverse (67.8% White, 25.2% African American, 5.1% Hispanic, 1.2% Asian American) high school students from 34 classrooms who provided questionnaire data both at the start and the end of a single course. Novel results from a cross-lagged model demonstrated that students who perceived their classrooms as allowing and encouraging their own autonomy in the first few weeks increased their engagement throughout the course, rather than the typical decline in engagement that was demonstrated by students in other classrooms. This finding is unique in that it extended to both students' perceptions of engagement and observations of student engagement, suggesting a fairly robust pattern. The pertinence of this finding to adolescent developmental needs and its relationship to educational practice is discussed.