I have a 9th grader and we haven't helped with any homework/studying this year or in middle school except for one math unit in 8th grade that he was having trouble with. I check in every couple of days with a "do you have any homework or studying you need to do?" but don't get more specific than that. I receive the grade reports every week from SIS and as long as his grade are reasonable and assignments are turned in (which they always have been), I let him handle it. I think it's important for them to be independent if able.
I also, though, would not let a 14 year old crash and burn without getting involved, so if that's the situation, then, yes, I'd be helping in some way. Setting up tutoring, making sure he is communicating with his teachers well, helping with homework or studying if I'm able, etc.
Every kid is different.