Students theoretically come to classes without knowing the material or skills taught in class. Since the teacher is meant to teach the student class material, it makes little sense to grade the students early on, especially before they have had time to master any skills. However, educators must understand where the students are at cognitively and what their background knowledge is in the material being taught, so teachers must give them some form of assessment that allows the teacher to plan what to teach in the class. These early assessments are formative.
Students need feedback to make changes on how they perform their work. For example, if a student does not correctly hit a volleyball in gym class, the teacher must assess what the student is doing wrong and then provide feedback on how to correct it. If students pay attention to the feedback, the teacher can gradually guide them towards developing greater skills.
Summative assessments are eventually necessary, as teachers give students grades that help schools determine which students are ready to move onto more advanced classes. Also, summative assessments make an education more valuable by ensuring that students who graduated with the degree really understood the classroom material. Summative assessments can be performed after the students have had time to learn course material and are most often performed at the end of the semester.
The instructor wants to know which pieces of classroom material must be retaught or taught in a different way. Students sometimes forget the material the teacher covers in the class, and the formative assessment can help the teacher assess whether the material is sticking and whether he is using effective teaching methods.
Formative assessments should be performed throughout the term. Teachers can even provide formative assessments at the end of the class, since students must take their knowledge and skills away with them. However, formative assessments are most crucial early on, allowing students to make quick changes to how they approach their assignments and projects.
Summative assessments are used to determine whether teachers are successfully doing their jobs. Students are often required to take standardized tests, and their success or lack thereof can indicate whether the teacher is using effective teaching strategies.