<p>For dartmouth, I'm writing my friend a peer rec...in the case that it actually turns out alright, would it be frowned upon for me to send it to schools like Princeton as a supplemental rec? Or are supplemental recs usually from coaches, summer instructors, etc?</p>
<p>...they're usually from coaches and others. but you can write one for a friend, tho, it's been done</p>
<p>the Princeton Optional Reference says </p>
<p>"The two Teacher References are a required part of your application. You may use this Optional Reference form if you wish to have an additional person who knows you well write on your behalf. That person may be, for instance, an employer, a music instructor, a coach, a religious leader, a parent, a brother or sister, or a friend. You may choose whomever you wish."</p>
<p>of course, coaches etc have more authority, but here if Princeton explicitly okays peer recs, i don't think sending one would hurt. it may even help your friend if you can write brilliantly for him.</p>