I have recently started doing proofreading work for an Educational publisher. They’re paying me around 100NT per page - is this excellent/okay/ridiculous?
Ridiculous.
What is a more reasonable rate to ask for?
It depends on the quality of the text. If you are just looking for obvious errors that rate might be OK presuming we’re talking 300 words/page. But if you’re rewriting/restructuring its not; you need to double it at least.
How much do you want to make an hour?
I’ll take a sample of the text from the middle and time myself on a page or two (usually I do this sample without pay if it’s easy, and show it to the client as an example of what I will do with the whole text, and have them agree to it before I take the case), then I calculate how many words I’m doing per hour, and charge them a per-word rate based on that.
I recently got a lot of work from a guy who wanted me to correct hundreds of short articles. I wanted my regular per-word rate and he wanted to pay me 100 per article, which I laughed at. Then he showed me the articles- they were well-written, just some small and easily corrected mistakes. Took about 5 min per article. 100 nt per article turned out to make me about 1200 per hour. I was pretty happy with that 
something I can do on my own time in the comfort of my own home and make more than teaching.
So yeah, it depends, but do time yourself and calculate pay based on that. As you get faster, you’ll make more.
Thanks for the advice. I re-negotiated, am now getting around 14,000 for 90 pages which will take me around 5 hours, so close to 3000 an hour.