Students' prior knowledge is both the basis of their further learning (Dodds, Griffin, & Placek, 2001; Wandersee, Mintzes, & Novack, 1994) and a component of teacher knowledge important in designing appropriate learning experiences (Graham (Ed.), 1995; Grossman, 1990) in physical education. The purpose of this paper is to examine students' prior knowledge of physical activity (PA) and physical education before the implementation of a teacher development initiative that promoted increased physical activity supported by the use of multiple assessments for data-based curriculum design within middle school physical education programs. Baseline data were collected from 72 students (representing 6 schools, 12 teachers) through structured 20-minute qualitative interviews. Researchers coded interview transcripts using open, axial, and selective coding (Strauss & Corbin, 1998). Results are organized around themes of students' perceptions of PA, skillfulness, physical education programs, and assessment. Students could describe both immediate and long-term physiological changes as a result of being physically active, noting a wide range of activities that develop fitness. They made clear links between high fitness/activity (which word?) levels and good nutrition and between junk foods and "couch potato" inactivity. Student perceptions of skillfulness derived from comparisons of self with self over time and with others and from others' feedback about their performance (e.g., teachers, parents, coaches). Students attributed their skillfulness to hard work, practice, and high effort; outcomes of being skillful included making elite teams and feeling competent and confident. The importance of practice and enjoyment were connected strongly to high skillfulness. Some students noted that physical limitations affected skillfulness (e.g., asthma, body composition). Descriptions of their physical education programs and of assessment (grading) procedures differed most among schools. For example, some programs included ongoing fitness activities as beginning class routines, while others included isolated fitness units. Students generated long lists of activities, confirming a traditional multi-activity unit approach across schools. While class routines differed across schools, most students could describe what they typically did during physical education. They sometimes confused instructional physical education with athletics and out of school physical activity. Grading criteria across all schools universally included effort and participation; some teachers also incorporated fitness and skill assessments, though multiple, varied assessments were not in place in any school throughout the entire physical education program. These baseline data confirm these middle schools as fairly typical and ready for interventions with teachers to increase physical activity and use of assessments tied to PA goals.Keyword(s): assessment, middle school issues, physical activity