I don't know what age 7th graders are, I used to teach special needs children in the 9 - 11 age group, and advanced pupils in the same age group. I always found, with both groups, that a good way to treat this problem, well, lots of other problems as well, is to take the line:
'that's good, (name), let's have a look at how we can make it excellent, if we...'
That shows the child that you're not hung up over the error and that it can be put right and the work looks better for it.
Contrary to popular belief amongst educationalists, kids care if they get it wrong. They would rather have a teacher show them how to do it correctly, than have one of their peers tell them and make fun of them.