Here's how I use them:
At the end of a lesson, I will have them show (using words, pictures and/or numbers, especially in math) one thing they learned. I typically do not have a class example, they will need to tell/show me what they learned all on their own.
Under that, I have them write one thing they want to know/still wonder about/want to learn/etc. This can be related to the lesson or it could be a tangent that was sparked during our class discussion.
Before they can transition to the next activity, I have them turn these in to me as their ticket out.
I always remind them that they will not be graded on this, it is just the opportunity to help "take the temperature" of our class- did we learn the important concepts or just skim the surface? What do we want to learn next? What did we think was the most important part? etc.
I also like to encourage them to write something in both sections- this takes a while to develop, but kids do write sentences in both after a few tries.
Here are a few examples after a lesson we recently completed after skimming Daily Life in a Covered Wagon to start our Pioneers Unit:
While I do not do these after every lesson, I do like to incorporate them here and there, especially if we are introducing some pretty complex concepts. Plus, I find it keeps kids more accountable to their own learning.
Do you use Exit Slips in your class? If you like my slip, feel free to download it here from Google Docs!!