What if each sketchbook assignment was worth a certain amount of points?
Let's say, a drawing: 2points
a drawing with color: 4points
However you want to "score" the drawings.
When students return in the fall you could tally up the number of points
they have earned. Perhaps they could then spend their points on little artsy
goodies your could either purchase or have donated. Like pencils, erasers,
I did this with sketchbook assignments with year and it worked well. The
students were motivated by bribery only at first. However, later they were
more self-motivated. I did this with 3-4 grades.
Hope that helps...
Oh!! And thank you, Jan, for you help with the Egyptian projects!