“Formative assessment includes both feedback and self-monitoring. The goal of many instructional systems is to facilitate the transition from feedback to self-monitoring.”  

- Sadler 1989

Since assessment data is always telling you something, even summative assessments are formative, meaning they should tell you if the students understood and can perform independently of your guidance. Even after an end of unit assessment, if students are still unclear of concepts or skills, they should be readdressing and reinforcing even as you move on.