Principal Letter of Recommendation

^ It seems to me that there are 3 options for getting a letter from your principal submitted:

  1. Have your principal submit a letter as an official "supplemental" letter of recommendation. That's straightforward, and an accepted path. A supplemental letter from someone who knows you well and can add insight beyond that in your teacher recommendations has value. This does preclude you from having someone else write a supplemental letter, as schools generally frown on more than 1 supplemental letter; but that may not be an issue in your case. From your description, it sounds like your principal does know you well and in a capacity different from your teachers, and could add value.
  2. Have your principal send an unsolicited letter. You cannot prevent anyone from sending an unsolicited letter, and schools will generally read what they receive. I had a teacher who knew me very well outside of the classroom send an unsolicited letter on my behalf (a long time ago), and I think it had a big impact on my acceptances.
  3. It may be possible for your principal to write your school letter in place (or in cooperation with) your guidance counselor. I had never heard of this, but Allen Cheng mentioned it in his admissions blog, and claimed that it had a positive effect:

http://blog.prepscholar.com/successful-harvard-application-common-application-harvard-supplement#principalrec

These are all options to explore with your principal and GC. Especially if your GC doesn’t know you as well as the principal, he might be open to pooling resources.