Progressive Training.
Set the initial bar so low that you cannot fail. Promise yourself that you will come home and do 5 minutes of schoolwork (or whatever). When you're comfortable with that, escalate. Set a timer, and when it goes off, stop.
You may be saying "5 minutes of homework is pointless", but the distance between nothing and something is a chasm. It's a lot bigger than the distance from "a tiny bit" to "a lot".