There are actually quite a few places that offer scuba diving classes in New York City. So if you are looking to get certified you can certainly get it done in New York City (is there anything you can't get in NYC?).
We took our classes with Scuba Network. We met once a week for 6 weeks. Class work took about 1 1/4 hours followed by about 1 1/2 hours in the pool. Our scuba diving classes New York used the pool at St. Barts.
To make the class cheaper, we opted to have a late pool time. So we didn't get into the pool until 9:30 PM (if I remember correctly). OK, we were younger and poorer then. But we really didn't mind it.
We were both very happy with our training. The instructor, Kathy, was very nice and very thorough. She took her time to explain things, both in the class and in the pool.
If you get a chance, try to meet your instructor beforehand. You might be able to get a feel for him or her. And if you don't like what you find, choose another operator.
We actually ran into Kathy when we were on a dive vacation in Cozumel, Mexico. She was leading a dive trip from the dive shop in New York. Nice job if you can get it!
If you plan on buying diving equipment for your scuba diving classes in New York, check their return policy. See if they let you try out the equipment in the pool first and return it if you don't like it.
My husband had a mustache when we took our classes. This made it hard to find a dive mask that didn't leak. Even tried the petroleum jelly on the mustache tip. It helped a little, but not enough.
Anyway, he was buying a mask from Scuba Network. He first tried them out in the pool during out class. I think he went through 4 or 5 masks before he found one that worked reasonably well.
Who cares that it is pink?
He is still using that mask today. Definitely makes him easier to find in a dive group. That and his orange scuba diving fins (but that's another story).
So, yes, you can find high quality scuba diving classes in New York City. Another reason to love the Big Apple.
So shop around and find an operator you are comfortable with. Relax, enjoy and soon you will be underwater.