Sort of like San D., I often ask another student if they think the "I'm
done" person is really done, and if not, what can they add/change/clean
up/etc. It is a difficult problem though. I had one student this year
that HATED art, and would literally tell me he was done with a project
the day we started!
This may sound bad, but my students are very grade driven. If they tell
me they are done, and they really do know that they just rushed through
it, but keep insisting they're done, I'll say "Okay, it's your grade"
Then they almost ALWAYS say "okay, I'll go work on it". I won't baby a
13 year old. They are responsible for their art as much as their math
and english. I need them to know it's now just an "easy A".