One of the most important points in the introduction of Formative assessment was its evolution from what came before it. For many years education was run off a system of Summative Assessment.
Summative Assessment is also known as Assessment OF Learning. This is a pretty easy way of undertanding what Summative assessment is. It is generally a way of assessing student learning through their final assignments of tests. This is a very useful technique is a few ways. It is absolutely useful when making a final decision of whether or not a student has accomplished a goal.
However, after years of exclusively assessing student work in this way, it became clear that this was not optimal. The main problem with Summative Assessment is that there is very minimal constructive feedback throughout the learning. As a result, by the time students receive their feedback, there is no room or time to improve on what they have been told. If the term/year is over, how as students supposed to take their feedback and learn from it?
That is where Formative Assessment comes in. A second way of thinking about Formative Assessment is as Assessment FOR Learning. Again, this name says a lot. It was created specifically with the goal of filling in the holes that Summative Assessment left, i.e. assessing and providing feedback for students with the intention of allowing them to learn from and improve on their work and learning.
This is a picture from the book “Classroom Assessment for Student Learning” by Rick Stiggins, Judith Arter, and Jan and Steve Chappuis. It is a table showing the differences between Assessment FOR Learning and Assessment OF Learning.