What I'm wondering is what is the story even about?

Let him know you love him and give him some constructive criticism. If you're like "that was good and i have ideas to make it better", he might be receptive. If it's just too bad, compliment his dedication and effort.

This I agree with. Back when I was in 8th and 9th grade I was on a crazy writing spree. Stories would just come out of me left and right, but all of them were over dramatic and lacking any real development. Yet fortunately enough I had the pleasure of always receiving positive remarks from the school librarian. She always encouraged me and now I can proudly say that I improved my grammar on my own because of the confidence she put in me.

Being nice to teens has created a generation (in the USA) that thinks they can take on the whole world, maybe some real criticism is better for him in the end.

Just be honest with him, parents are supposed to help their kids improve :)

Which is probably not going to go over well. People SHOULD accept constructive criticism, but they usually don't when it's something they've spent a lot of time on. Especially not teenagers, and especially not from their parents. OP's probably going to have to fake being the supportive parent, or deal with his son's hurt feelings for a pretty long time. It's not like the kid's going to go on a talent show and completely humiliate himself in front of an audience, the worst scenario would be that he sends it to a publisher and gets a rejection letter stating that the novel is 'not what they're looking for right now'.

I'm actually 16 and writing a book and I ask people to read my work and give critical feedback so I can improve it. I don't want to hear things like "oh that's great" when I know it can be improved, because as the writer of a piece you tend to skip over small grammatical errors and stuff like that

Yeah, I don't know what you're talking about, 26. I loved getting constructive criticism from my mom as a teen, especially with writing. Parents know what they are talking about and my mom always had good ideas about how to make it better. The trick is just to complement it first and then suggest things to make it better as opposed to just saying "your grammar made my eyes bleed"

if its just grammar mistakes they can be easily fixed, but if its the content that is bad... sorry op

26, I doubt it. I've been working on a novel since I was 15 (I had to start completely over when I was 17 due to a house fire though)and have always been very picky about who I show my work to. The people who annoyed me most were the friends who consistently told me, "Oh my gosh! This is the best story ever!" Nice ego-booster but not a lot of help. The people who became my closest friends in high school were a group of other writers who critiqued my story and expected me to properly critique theirs. A real writer who cares about their work needs criticism and knows it, and I'm sure OP's son will appreciate some help.

It's the same way with music too. You never want to hear that It's great. You want someone who can form an honest, constructive opinion on it to help you better yourself for any future creations. Be honest, OP, and try to help them along.

#53 Not every teen likes hearing constructive criticism from parents. I actually think #26 has a good point. When I was that age, I found it easier to take criticism from my teachers than from my parents., possibly because I didn't have to live with those teachers.

Not only teach him, but realize that at least while other teens are out doing drugs your kid is trying to write a book

In the kids defense he was probably not even a teenager when he started the book, and if OP is only a couple pages in chances are he wrote those pages 4 years ago. I'm sure as you read on there will be a noticeable difference in his writing skills.

How do you think writers cope with 4 years of writing drivel?

I heard the son's grammar is so bad it's driving OP to do drugs.

Twilight 5: Jacob gets arrested for child molestation by OP's son

Maybe it starts with a 12 year old's grammar and he hasn't gotten around to fixing it. The end of the book could be perfectly fine.

"12 year old's grammar" 12 is a lot older than you think.