Few physical educators engage in formal assessment of student learning outcomes. Recent trends in high-stakes teacher evaluation make formal assessment of learning progress/outcomes by physical educators a teaching function, central to a "well-rounded education" through recent federal legislation. This project targeted the following research questions: (a) Can physical educators increase their use of formal-formative assessment of student learning outcomes as a consequence of a professional development intervention that includes on-site coaching support? and (b) Can physical educators reliably collect formal-formative assessment data on student learning? Seven (4 females, 3 males; experience range: 4-15 years) licensed secondary school physical education teachers volunteered as participants. The intervention included professional development (PD) workshops, ongoing on-site coaching support, and prompting. A multiple baseline design (MBD) across subjects determined the efficacy of the intervention on teachers' use of formal-formative assessment practices. Postcheck follow-up observations were made during the following school year. Data were collected via the validated Systematic Observation of Formal Assessment of Students by Teachers (SOFAST). The reliability of teachers' use of formal assessment was established with a second trained observer simultaneously collecting identical data on the same aspects of student performance as the teacher. Data were plotted graphically across sessions and assessed with standard visual analysis criteria, which demonstrated the functional relationship between the intervention and teachers' use of formal-formative assessment of student outcomes. Standard interobserver agreement calculations determined the reliability of the teachers' assessments of students' MVPA levels versus outside observers' via the total interval method. All seven teachers increased their use of formal assessment of student performance and shifted focus of the assessment toward subject-matter performance. Their formal assessment observations were found to be reliable. Experienced secondary school physical education teachers can successfully and reliably employ formal-formative assessment of student performance outcomes.