I second contacting the teacher and asking for the students to be separated at lunch. I would think they could sit at the same table, just not next to each other. Surely someone could tell the children not to sit next to each other and whoever supervises the lunchroom could check to make sure they are not.
At our school the vice principal handles discipline, and would be the person I would contact if the teacher didn't resolve the situation. Most schools take bullying very seriously, and even if the child is not doing this out of malice, if your son doesn't get to eat his lunch it IS bullying.
