This is a wonderful took I use all the time to check for students understanding. This is a great exit slip for at the end of the lesson or could even be using during the lesson once the instruction part of the lesson is over. I simply give the students the exit slip and the have to fill it out and hand it in before we transition to the next subject/activity. The students fill out one of the sections. If they completely understood the lesson they would write what they learned in the green light section. If a student understood most of the lesson but is confused about a certain section of it then they write what they are confused about in the yellow light section. If a student is completely lost and does not understand anything they write where they got lost or what they don't understand. I then look at what the students write to see what I need to revisit the following day or if I can move onto the next lesson. Sometimes you might see a handful of students that have the same need so then you can do a small group instruction for those students. I left this as a word document so that you can change the wording of each section or change the title to whatever you desire. I hope this assessment tool helps you to guide your lessons based on the students needs!