Use of the interview as a formative assessment tool has a long history and includes connections to the related fields of mathematics and special education (Weaver 1995; Ginsburg 1997; Fennell 1998). Our motivation for including the interview technique as one of the CBFAs is that it provides the obvious follow-up to an observation a teacher might make when implementing a lesson. An interview allows the teacher to spend a few valuable minutes "digging deeper" with an individual student or perhaps a small group of student. In our continuing work with these CBFA techniques we have found it important to communicate that the use of an interview is not based on a deficit model. the interview may occur because of a particularly creative or advanced response just as easily as it may be a response to a misconception. In essence, the goal of the the interview is to get a glimpse of what the child is thinking. We have used the questions below to help guide the use of an interview.