We're homeschooling now, too, but  when my son went to school they had a special table for kids with severe allergies.  They actually had about five small tables and the nurse assigned kids to each table according to what they were allergic to.  Unfortunatley with dairy sometimes one kid sat alone because it is hard to find other kids who don't have dairy in their lunch.  Basically, anyone sitting with him would not be able to have spillable dairy like milk or yogurt or you could request no dairy in any form at his table.  At my son's table, kids couldn't have peanuts or seeds.  Usually most schools have plans in place.  I would call the school nurse and ask about what their policies are and how they would handle it.    Another idea is to have him at his own special table and to have a lunch buddy to eat with each day.  Perhaps you can coordinate a lunch buddy schedule with the teacher and send home a note to parents stating that their child will need to bring a dairy free lunch to school on their designated day.  Some kids will forget and he may have some days eating alone but it is better than eating alone, especially since lunch is such great social time.  Another idea is perhaps you could have your child eat in a separate room with a therapist and knock out some therapy time integrated with lunch.  Not perfect but productive.