A variety of methods that teachers use to evaluate their students' comprehension, learning needs, and academic progress DURING a lesson, unit, or course.

The purpose of a formative assessment is to help the teacher assess their students throughout a lesson to see if they need to go back and explain more on certain topics. 

Evaluation of a student's learning at the END of a unit which is compared to a standard to determine comprehension and retention. 

The purpose of a summative assessment is to help the teacher see if their students have understood and retained all the information that they were given in a specific lesson, unit, or course. 

The difference between a formative and summative assessment is when and how often they take place. Formative assessments are going to be things such as homework assignments, in class work, or quizzes that the teacher does pretty frequently throughout the class. On the other hand, a summative assessment sums up everything that was taught the entire lesson, unit or course. Summative assessments will typically occur a lot less frequently than formative assessments and are most commonly seen as a test, exam, midterm, final, presentation, or a large project.