Crazy parents
According to the OP, who worked as a counselor for struggling kids and teens, the source of the children’s problem is their parents. Living in a certain environment will leave its mark on anybody, so if you act out, your children will adopt your behavior and unleash it in class.
Students from elementary and high school will do better in class if their parents show some interest in their studies. If they don’t, then the kids will most likely not take the initiative to do better academically. If a parent gets angry for the tiniest reason, their little clone will learn to lash out when something goes wrong even slightly. Do your kid a favor and don’t just tell them how to act. Show them.