Ms. Lilia Olivas introduced her fourth-grade students to the idea of counting how many cards would be exchanged if everyone in a group of 24 gave a card to every other person. This led to a problem very similar to the one you just worked on. In the video segment at left (duration 9:05), you can watch Ms. Olivas's students as they try a variety of methods to figure out this problem. Note in particular the evidence of students using reasoning and justifying their thinking and solutions. Think about how your own students might tackle this task.
Please watch the video excerpt now.
Think about the classroom you observed