Hello everyone,
I was wondering if a letter of recommendation from a peer would negatively affect my chances at admission. At some schools, we have the option to submit multiple external letters of recommendation, I already have one from my employer and have the space to add another. Since my friend is already writing one for me for Dartmouth, I was wondering if it would hurt my chances to add it to other schools as well, where I have the option to add another letter. Let me know what you guys think.
“At some schools, we have the option to submit multiple external letters of recommendation”
You don’t want to water down your app. To me, Dartmouth is the odd exception – the peer rec works for them. 1) I find it odd that many other schools want “multiple” external LoRs --what schools are these? 2) Rule of thumb is this: send supplemental ONLY if it adds a powerful and different perspective than your 2 teacher LoRs. I highly doubt a peer can supply this. Usually, this is for a research mentor, employer, clergy person, coach.
You don’t want to water down your app. I wouldn’t do it.
Unless a school requires a peer rec (a la Dartmouth) it’s almost certainly not wise to send one in.
^^^^I agree. Unless it is specifically requested do not send a peer recommendation. Dartmouth is an unusual in asking for that.
And there is no need to fill up every space on the recommendation request – unless you put in another adult who can add to your application by providing information that can’t be found elsewhere (perhaps a teacher you work closely with in a club, an orchestra teacher etc.) then leave that last line blank.
Thank you for the advice! I’ll only use the letter from my research mentor for other schools.
I agree that’s a better choice. Look at the required letters, not the optional spaces when considering to add another letter or not. I think it is better to err on the side of caution.
I think if your peer is “that” credible it might increase your chance of getting into the university you prefer. 
I think if your peer is “that” credible it might increase your chance of getting into the university you prefer.