I've taken online classes through my work--these are self-paced modules were you read the material, test your knowledge, and then take a test. Some come with additional information, like for a grammar one, there was a list of typical jargon words. I've been surprised to see how much I've gotten out of some of them. But there have also been a few that just didn't do much for me, and others that were in between.
I'd suggest instead of taking a generic "How to write a novel" class which covers a very broad topic, maybe look for ones that cover a more specific area. I did a viewpoint workshop last year that turned out to be helpful--all it focused on was all the different viewpoints.
However, I do think one of the problems with the writing ones is that if you don't agree with the instructor's perspective or your writing doesn't fit in with the direction, then it's not going to be a good session. I did one on description that I felt didn't help or offer any new insight because the instructor had a very specific image of how description should be. That, combined with the selection of exercises, didn't allow for much flexibility to learn anything.