When I was introducing shapes to my 1st grade students I this year assumed that they did know many of their shapes due to their kindergarten and 1st grade math curriculum. But I didn't want to assume they were all on track without a quick assessment. I choose 6 simple shapes (circle, oval, triangle, rectangle, square and rhombus) to ask student to become the experts with and teach others. I gave each class a bag filled with manipulatives that they were asked to develop and then share with the rest of the class what the shape was, and how it was made.
As you will see in the video below I asked the students to go from table to table to learn about the shapes from their peers. When this 20 minute lesson was done we created and learned about more shapes using shaving cream (see previous post).