Disclaimer: Mine is just a 7th grader, not sophomore, but this is something I've been struggling with too.
I realize this is an extremely simplistic partial-answer to a complex question, but I recently got the book unJournaling. It's just a collection of writing prompts with a fun or creative bent. It won't teach how to write or grammar or anything particularly vital, but it DOES seem to be opening my 7th grader up to the writing process. It is NOT our writing/grammar program (we use Hake), just an extra something to loosen up the whole thing.
Like SailorMom, I have trouble teaching writing because I picked up good writing methods from the books I would devour. My 11 year old daughter, also a bookworm, is also an excellent writer. Her 13 year old older brother, OTOH, has a really difficult time. Reading is difficult and he avoids it whenever possible. So, by extension he has never picked up those natural writing tendencies. It has always been a struggle. He can recite grammar rules and diagram sentences, for example, but when putting it into practice in his writing, there seems to be a complete disconnect.
His spelling is atrocious, he forgets words, he puts punctuation in completely arbitrary locations...It drives me crazy. His sister stands behind him when he's emailing friends so she can make sure he's saying what he thinks he's saying! lol
Til now it has always been a fight getting him to write. A natural story-teller, he likes the creative process, but the transfer onto paper is painful.
unJournaling, however, has been fun. Truly.
His journal is in an OO document (since his handwriting is completely illegible). He types his 2-3 paragraph response and then goes off and does something else. Later, we sit down together and read this thing.
I make him read it to me, so he can see how difficult it is to pick through as is. Then we go about fixing everything. I make him leave the original and we just paste another copy directly below it. I want him to be able to see his progress. And because of the brevity and fun topics, he doesn't seem to fight the dissection of his work like his does his English papers. We'll see how long the novelty lasts, though. ;)