Another way to do exit slips
A stoplight and a bunch stickies -
Green: an idea they learned. Red: something that is stopping them from "getting it". Students put their post-it notes on the yellow light in the form of a question, or an idea they are curious about but haven't really wrapped their heads around yet. The teacher can share results by either talking about common patterns or projecting a few of the responses the next day.
Alternate format - use coloured baskets with index cards rather than post-its.