Our Diamond section was pgs 79-83 in the Comprehensive Curriculum of Basic Skills for Preschool. We traced, colored and wrote the word diamond.
For our first project I gave J triangle stickers and asked her to figure out how to make a diamond out of them. It took her a while so I gave her a few hints as we went: use only two triangles, have them touching, have one pointing up and one down and. I also ended up drawing a diamond to help her along. I had to use some self control to not move them around for her but she was very proud once she finally get it for herself! (If you want to simplify you could just start with two larger triangles.)
Second, we made kites with Glad Press n Seal and tissue paper pieces. You could also use contact paper if you'd rather.