I've used this recipe with my grade 6 & 7 students, but it is a fun lab for any age.
Students work in groups of four to create turtle shaped sugar cookies. One pair creates a white dough, and the other a green; and work together to combine them to shape turtles. The back of the recipe includes a few theory questions that relate to the skills and vocabulary used in the lab, to check for understanding.
The recipe is written for two 40 minute classes. It can be done in one full length class, as long as there is time for the dough to chill.
This lab will definitely be popular with your students!