You can use this simple protocol as a bell ringer or exit ticket. It has three parts:
Now: Something they've learned recently
Then: Something they learned not too long ago
Way Back: Something they learned a while ago
The teacher can choose the topics, or the students can. The topics can all be related to something students are learning right now, or they can be completely separate. Students recall three things in each category.
Want to know more? Check out this blog post.