I’m a junior in HS and my friend is currently banging out some last-minute college app stuff, particularly all of the writing. He’s an average writer, I’ve been told that I’m a pretty good one. I really want to help him with his essay and supplementary questions. I understand the ideas that he wants to get across and I don’t have any intentions of trying to silence those; I want more than anything for his ideas to stand out. But I know that essays are supposed to be your own. My English teacher spends hours of class time critiquing student sentences and restructuring them (and encouraging us to do the same) to make them more concise and readable. To what degree am I allowed to do that to someone else’s essay? Where does the line get drawn? Is it ok to recommend how to organize some ideas? How to restructure a sentence or combine two sentences? Please help. I’m terrified of overstepping and making it sound like nothing he’s written is his own idea.
Personally, I don’t think you should be helping your friend with his essays. As a junior in high school, I’m not sure why you’d be any better qualified than he is to express his own ideas. Leave the (minimal) help to the English teacher and other experienced adults.
I think it would be cool to give ideas, but not physically edit it. Colleges can see the differences in two writers, and it would probably bring up red flags.
I also think grammatically errors are safe to offer suggestions on.
I think proofreading using fresh eyes is always a good idea, and you can point out stuff that doesn’t work very well, but the solutions should come from his head, not yours, and the corrections should come from his fingers, not yours.
You’re a good friend for wanting to help 
Agree with MoD. Nothing wrong with discussing, but realize it takes some self control not to insist or dictate. In the end, it’s not about your idea of “better,” but what he’s satisfied with, when he submits. That way, he’s confident he tried his best.
I think you should leave his essays alone. They’re his, not yours. If you think he needs help, suggest he show them to his English teacher. I’m sure s/he will be happy to read them and offer suggestions.
Grammar is one thing you can do without overstepping. Giving ideas, telling if a sentence is awkward is good too. By giving ideas I don’t mean researching the uni yourself and pitching out programs they have lol, more like, “you should expand on this. Cut this out because it is repetitive. Mention yourself benefitting in the college.” things like that
Also, the time commitment you want on your friend’s essay is up to you. If you want to review it for 5 or 25 minutes or minimal help or extensive help. Peer edit as if you’re in an English class because in English class when you edit some else’s paper it’s not completely rewritten.
I wouldn’t worry too much unless your friend tells you to back off.
On a side note: My brother rewrote my essays and threw a tantrum because I didn’t adopt them. Don’t throw a tantrum if your friend doesn’t accept a lot of your suggestions (if you decide on the extensive route)
I have edited a lot of my friends’ essays, and worked as a Writing Tutor for the past two years, so I have some experience with this topic. As long as you are not changing his ideas, and the solutions ultimately come from him, you are free to offer suggestions. Sentence clarification/grammar, go for it- oftentimes a fresh pair of eyes can spot funky sentences better than the writer.
Since this friend is “banging out some last minute stuff” have OP suggest the friend go to see the English teacher seems an unlikely solution.
@abbidon Read the prompt and the essay. Proofread the essays for your friend and make sure the essay addresses the prompt. As you read the essay, if something doesn’t make sense to you or you notice your friend uses a particular word or phrase too often, note it. General guidance will be fine.
I agree with the above. What everyone here is advising is ethical and noble, but it’s important to note that there are also families who pay tens of thousands of dollars to consultants to construct essays for the students–with student input of course.
I think it’s fine to give feedback like"this transition feels abrupt" or “I was left wondering xyz” or even, “this doesn’t sound like the person I know.” It’s even okay to note grammatical errors. But you should not write a word of it. This is his essay, not his good friend’s essay.
I would say never to suggest any new ideas or material. Limit yourself to pointing out grammar or punctuation issues. It should be completely your friend’s own idea, and if they can’t figure out what to write they aren’t ready to apply. The whole point is to reflect that particular applicant’s point of view and provide insight into who they are as a person.
Wow, thank you so much for all of your answers.
@CougarCatClan Definitely no tantrums here, if he gets in or gets rejected it’s on his own merits and not my writing.
@elliebham On break, deadline before it ends, he’s in regular and I’m in AP, but I get your point. He’ll definitely get it reviewed by a teacher for schools with later deadlines.
@jpgranier @CorpusChristi Yeah, I wouldn’t suggest ideas beyond what he thought of. Reorganization of sentences and existing ideas at most. AO’s are there to decide if you’re a good candidate, so giving him brand-new ideas wouldn’t allow them to fairly evaluate him at all! 
@MotherOfDragons Thank you, I really am trying to just help out. Laissez-faire is kind of difficult for me but I’ve learned pretty quickly how to teach him to make edits rather than make them myself.
@paveyourpath @Dustyfeathers @yonceonhismouth I feel like you guys get it. Definitely hard to keep my hands off since a good quarter of my English class is spent rewriting other people’s sentences to be more concise, so I’m minimizing it to improving phrasing, pointing out where two sentences could be one, etc.
Thank you everyone who answered. If you don’t agree with the help I’m giving please understand that I’m not giving him any new ideas (except on one of those “name something positive about yourself” questions, since…well, he’s working on identifying those traits in himself). Compressing what should have been weeks/months of edits into just a couple of days has been pretty challenging for both of us but I can now better see the line between efficiently editing and brazenly overstepping. I can identify where I went too far in making suggestions and I’ve made sure to have him go back and take note of general structure but rewrite things in his own words. It really, really does sound so much better when his voice is clear. Thank you again for all of your answers and I’m sorry if I missed anyone in this response.