Small Group Instructional Diagnosis (SGID) is a "classroom as focus group" process where a colleague of the course instructor collects students' perceptions of the course through a discussion with the students. SGIDs are scheduled mid-semester when changes can still be made. Often SGID data encourages instructors to explain their rationale for various decisions made about some of the following: the course text, student-learning outcomes, teaching-learning activities, assessments, or grading practices.
See Cynthia Desrochers' (Elementary Education) fall 2001 CELT Letter article for SGID history and CSUN faculty testimonials:
"S.G.I.D. -- Tapping Student Perceptions of Teaching" 
Also, see Nancy Diamond's* article, "S.G.I.D. (Small Group Instructional Diagnosis): Tapping Student Perceptions of Teaching," from chapter 14 of POD Network's book, POD: A Handbook for New Practitioners.
* Nancy A. Diamond is an education specialist in the Office of Instructional and Management Services at the Unviersity of Illinois in Urbana-Champaign.