Child Has Severe Allergies To All Animals, As Well As Outdoor And Indoor Allergies, Feels Lousy. Suggest?

My son has severe allergies to all animals, as well as outdoor and indoor allergies and is struggling. We have the allergies controlled at home, however they act up at school. What in the schools could be aggravating them? They had issues with mold a few years back but have resolved the problems and says the air quality in the school is good. They have an air filter system with ultra violet light which is suppose to kill allergens, as the air conditioning pulls in outside air and recirculates into the school. I don't know what to do, my son is constantly distracted because of how lousy he is feeling and therefore doesn't concentrate in class. The schools answer is to hold him back, but I strongly believe his medical problems are the culprit.