Negotiating an offer, is it too late?, teaching assistant here

I received an offer as a teaching assistant and I think the pay is a little low. Any experience at all would help. I have a competing interview next week. What wording worked?

Thanks for writing this out. I went through something close to it 12 months ago, and it got easier once I kept a simple log of every call and form.

Keep everything in writing and save the confirmation numbers. It made the follow-up calls so much easier.