"""but does anyone think 6th grade is too young for this? ""
The 6th graders I was working with did a very successful water color lesson. We did barn paintings rather than seasonal still lives, but I think the process is more or less the same. The key to the lesson was to be sure that the sketches were very detailed. Before the kids painted, they went over their lines with black sharpie markers, then painted one section at a time (one board or shingle), mixing at least three colors in each section. That way, it was had enough structure for kids who are still pretty concrete thinkers.