Actually, to be clear, for the Common App, the GC fills out the School Report, which is basically checkboxes and fill-in-the-blank, **and/b an LoR which asks:
• How long have you known the student, and in what context?
• What are the first words that come to mind to describe this student?
• Please provide comments that will help us differentiate this student from others. Feel free to attach an additional sheet or another reference you have prepared for this student. Alternatively, you may attach a reference written by another school official who can better describe the student.
Please check here if you will not be sending a letter of recommendation with this form
As mentioned upthread, the admissions sites for the colleges will detail what type of LoRs are required.