I recently read an article on Kindle's page in Facebook that asked this very question. Although the author of the post believed that writing classes won't make a difference, I beg to differ.
I am sure there are hundreds of thousands who want to write books, but have been out of school for years - like I was. I really needed a refresher course in creative writing and am very grateful for my writing coach. She reminded me of certain skills I had forgotten and encouraged me to continue on in my quest to write a book.
I have seen people use the excuse that some writers have a different style of writing than others so however your book turns out it's fine. To me this says, "I'm too lazy to make sure my book is clean and tight for my readers".
Yes, it is true there are as many different styles as there are writers, but it doesn't mean your writing will be enjoyable, or even tolerated by the reader. If they put your book down then all the work you did was for nothing. I realize your book won't be for everyone, but if it's a reader that enjoys your specific genre and simply can't continue reading due to all the creative writing mistakes, then you need a writing class.
I remember being contacted by a writer online who told me his writing was so bad when he self-published that he pulled his books and took classes to improve his writing. After revisions and cleaning up his mistakes he was so happy to have his books back on Amazon and his sales were going great.
Just because you need help with creative writing skills doesn't mean your story isn't good though. This has nothing to do with that. It's about molding the story so that the reader will enjoy it. I always knew I had a good story, it just needed cleaned up.
So the next time someone tells you that you don't need a writing class or even a critique partner know that isn't true. Sometimes I wonder when a writer gives advice like this it's to weed out some of the competition out there. After all, there's more books published now than ever in history because of self-publishing.
Don't get discouraged and there's nothing wrong with reaching out for help and guidance. If they are supportive writers they will always give good advice and help you along in your dream of becoming an author!
If you've ever run into this leave me a comment and let me know. I would love to hear from you.