Most schools operate a three-step complaints policy - the school, then the Govs, who will have to set up a panel of govs which must not include parent govs who have children in the same year as your child or any staff - they will be interviewed by the govs and make a statement, as will you. They have to meet within certain timescales, and respond within certain timescales. Next step is the local authority, and if you're still not satisfied, you can appeal to the Secretary of State for Education, but you must have gone through the three-steps first.
The Govs panel ime (I'm the school manager in a primary) is a bit of a glossing over exercise - the complaints we've had made against the school tend to come out a draw. The govs will say something like 'the parents claim was upheld as she DID feel insulted by the teacher, but the govs equally find that the teacher did not intend to be insulting' sort of thing, so be prepared for that to be an empty exercise.
It's such a shame that your poor son has had to go through all this - in my borough we are forbidden to administer medication, but we have alarm clocks to in the office to shout up the little 'uns to take their medication under supervision. All medication is kept in the office, clearly labelled with the child's name and details of the dosage. It really isn't an insurmountable problem, to be honest.
Hope his new school are able to be a bit more pro-active, Shiftybaglady - though 850 kids is a bit 

for a primary - I've got 450 and we're the biggest in the borough!