Lots of people love Brave Writer.
At what age is he hoping to start online college classes? I would try to downplay the idea that he'll struggle with college courses. While the charts and lists don't say this, it's actually pretty common for kids of this age to really struggle with writing. When push comes to shove and they are about to enter college, they usually figure it out. Sometimes it just takes some simmering and steeping, if you know what I mean. Some exposure and time for the brain to assimilate.
Does he like to tell stories? What excites him? What does he like to tell you about? Has he tried dictating into dictation software? Then he can edit. Sometimes that's a boost.
My dd is taking an online writing course at
www.udemy.com It's only $10. She's learning a lot. She's 14, though. It might be too much for an 11 year-old. She's taking creative writing now, academic writing next. So far, the assignments are SHORT, which makes her happy. But she feels like she's learning.