What is it?
A formative assessment can be used when a child is at a roadblock in learning the content of the lesson being taught. It is more of an assessment of the process in learning new material as opposed to the product.
Why is it used?
Their primary purpose is to inform teachers about how their students are progressing, where gaps exist in students’ learning, and how their instruction needs to be adjusted to improve student learning, possibly by slowing down the pace, repeating instruction, or even challenging some students with new and potentially more difficult tasks.
An example of a formative assessment would be a pop quiz to get an idea of what the students know and what pace you should continue to teach at to promote the best efficiency. Some strategies would be questioning techniques or modifying them on the fly. Other examples include hand signals, index cards , brain dumps, and three minute pause. (Marco)