Here's a sample request for evaluation -
http://www.studentadvocacycenter.org/sampleletters/special_ed_eval_request.shtml
There's a ton of other samples here -
http://www.studentadvocacycenter.org/sampleletters/index.shtml
In my experience, a request for a sped evaluation is sent to the person in charge of sped for the district. Since that person is not going to be in your mtg tomorrow, I wouldn't bother giving any of them the letter because they can't do anything about it anyway. I probably
would advise them that you are requesting an multidisciplinary evaluation/ARD (it goes by different names in different states) to define any special education needs your son has.
The reason for the certified letter is because that starts the time line. I think in one very extreme situation, I did hand deliver a letter to the sped director's office and had her secretary sign, but realistically that is only saving you at most a day or 2.
Since I assume you're mtg with the "not my problem" teacher, I wouldn't expect too much out of this mtg. *Maybe* she was just having a bad day that day but.... well, I'm a pessimist by nature so I always tend to expect the worst. The school is not obligated to provide diddly-squat without an IEP though and they're perfectly within their rights to say he has to sit at the back of the classroom, not tap his pencil, keep his legs out of the aisle, etc. What possible good can come out of these requests is a bit beyond me, but... sometimes school staff can be just as challenging as our kids.
Take very good notes during the mtg - who said what. If there is anything that comes out during the meeting that you disagree with or that you think might be a problem in the future, you need to send (certified, always certified) a letter of understanding to the parties involved in the meeting as well as sped director, with the request that your letter be filed in your son's "permanent" record. This letter should just be documentation of who said what, what you disagreed with, and why. No emotion, nothing more than a factual statement.
If you don't have copies of his referrals, you need to get them. It's time to start keeping meticulous records.
Good luck, keep calm, document, and let us know how it goes.