The difference between formative and summative assessment lies in their purpose and timing. Formative assessment occurs during the learning process and is used to provide ongoing feedback that can improve teaching and learning. In contrast, summative assessment evaluates student learning at the end of an instructional unit by measuring their understanding of the material. Formative assessments can include quizzes, discussions, or projects, while summative assessments typically involve exams or final projects, both serving critical roles in gauging educational achievement.