At times some of my sims children will just do homework autonomously without any persuasion from me.
Hah, in the first sims game bad grades meant your child being sent off to military school. Harsh~
I have had let a teen not do their homework for awhile and just go to school doing the 'normal' pace and their performance did keep going down, but not as harshly as if I had them talking with friends or goofing off. Usually when they're in a bad mood it goes down more.
I kinda would like to see teens able to just drop out of school or just runaway for awhile until it gets remedied by the parent.