The heart issues may need to be addressed. If this is the case, you may do well to talk with the key offenders separately. You will need to invest much prayer. There could be some spiritual warfare going on. Satan does not want your students to learn.
Distractions are a prime tactic.
If you sense this as a possibility, get to class a little early and pray over your room and for specific children. Keep it up until there is a break-through.