To me, I think there are more germs at schools than anywhere else. My son was really never exposed to other kids until he was around 2 1/2 years of age. Then he got sick occassionally. When he started preschool at age 3, he started getting a lot of unexplained fevers as high as 104 and 105. Thank God I was able to control the fevers and I took him to the doc quite often that year. This year was his second year of preschool, and he didn't get sick as often, but still had the occassional unexplained fevers. My pediatrician said that it usually takes kids about a couple of years in preschool to build up their immune system. She said if I hadn't told her that his fevers had subsided this year, that would have caused her some concern, but since they lessoned this year, she is sure that it is just his immune system building up. She even said that when kids get into preschool that they usually get sick quite often. Kids go to school sick, with runny noses, coughing, diarrhea etc. It was shocking last year after his first year of preschool and my son getting sick at least twice a month just about, that summer he never got sick once! Then of course when preschool started again, so did his illnesses.
You can do an immune test on your kiddo and see if there is something wrong there. But, your pediatrician may tell you to wait another year for your child to be in school for two years to do any out of the ordinary tests. Just depends on your doc and what he/she suggests. Your home is a lot cleaner than any school environment. Kids are still learning hygeine and washing hands often etc. So, they are going to spread germs like crazy at schools. Even with the janitors cleaning up each day, still won't be as clean as your own home. :-)
Are you giving him a vitamin every day? I give my son a Flinstones vitamin each day. And that doesn't prevent him from getting sick, but it does help.
Talk to your pediatrician about Aloe Vera Juice and giving it to your son. Aloe Vera Juice has a lot of healing properties in it, and it is well known to really help your immune system. Talk to your doctor first about this before you decide to start this remedy. I'll send you a link to a website that will help you understand this better. The article says not advisable for children, but it didn't state at what age. On our bottle, it says you can give it to children of five years of age. Here is that link:
http://www.americanchronicle.com/articles/view/29154
Hope this helps. :-)
PS: Berries have a lot of antibodies in them and these can really help the immune system. :-) I got this info from my OB/GYN. Lots of different colors of fruits, including berries will help a lot.