I am in the same boat (we're doing Altered Books, too!) And yeah...
most of my boys are in Art because they didn't think they would have
to do anything for that A... unlike keyboarding which requires some
sort of effort. Ha!!! They were royally ticked-off when they
realized that art is a lot of work!!! And you have to do stuff at
home, too! And you even have to (gasp!) bring stuff in to work with!
I'm so mean.
Anyway, I've found that the biggest motivator for these guys is
grades. Most of them play sports and need to keep the GPA up. Often,
I will pull them aside when they're acting goofy, show them the rubric
for the project, which lists (in exquisite detail) everything they
need to demonstrate to me to get that A, and explain to them that,
while I'm giving them tons of artistic freedom, there are some
guidelines that they have to stick to, and that, while their goofiness
is definitely entertaining, it doesn't demonstrate to me the skills
and knowledge that I need for them to be learning. IF they want that
A, they have to do all the things on the rubric at the A level.
Getting upset over goofy behavior just makes them want to do it even
more. Keeping my responses purely logical and unemotional seems to be
the best way to get them to take me seriously.