In both of my kids' schools, teachers make an effort to allow extra credit and retakes so kids can build back up from a disappointing grade. This sounds like a good idea in theory, but in practice, it doesn't work out, at least for my kids.
Last year, Older Daughter had a science teacher at Friends Omphalos who was proud of all the opportunities he gives his students to amass extra credit. For Older Daughter, it just looked like more work when she was already overwhelmed by the workload. She isn't that motivated by grades and credit in any case. She never did any extra credit work, much to the teacher's surprise.
Younger Daughter had a geography test at the beginning of this year (3d grade) that she flunked. Looking at it, I was actually surprised that she had the patience to complete the test -- it was quite long. You could see that at a certain point she just gave up and started writing anything at all so she could say it was done. Surely she doesn't actually believe that the direction between North and West is called "eastSouth"?
The teacher tried to give YD a chance to re-take the test, on the grounds that it would boost her confidence to do better, but YD refused. She also refused to study geography more at home. She'd rather just forget it ever happened.