The school year is winding down for me (I only will see each group of students 3 more times) and that time will go quickly. So as the end of the year goes by I try to keep projects as a two day lesson because with end of year field trips, field days, and assemblies there will be several groups that will miss. Here's a Wayne Thiebaud lesson that most students were able to finish in two classes. I did a Theibaud lesson last year with 4th graders and really loved the results as far the variety goes. For another year I may try to combine the two.