@Zero OmegaOnce your kids get an A grade, you can switch their mode from Study Hard to Make Friends, allowing them to meet new sims in the child and teen stages.
They accumulate Vacation Days, too. Just have your kid phone it to take a "Vacation Day (School)."
If one of your household sims has at least Level 3 Writing, they can "Write...Excuse Note" for your kid to skip school for the day. I'm not sure but the cooldown might be every two days.
I don't mind my sims going to school until they get an A grade. It's also a nice break from controlling all the sims in the house.
Also, doesn't doing homework raise a grade-school child's Mental skill?