A model for analysing the nature of the dyadic teacher-student interplay in instructional situations including one teacher and one student is described. The "teacher" may be a regular teacher, a parent, or any other person who is in the position of teacher. The "student" may be a student of any age. The model may discern (a) if the teacher merely asks for information preknown to the teacher and the teacher evaluates the student's answer according to the teacher's preknowledge, (b) if the teacher asks for information preknown to the teacher, the teacher then scaffolds the student's learning by giving clues to the correct answer and then evaluates the answer according to the teacher's preknowledge, or (c) the teacher asks for information not preknown to her/him and the teacher is genuinely interested in the student's answer. This last scenario (c) is thought to give optimal conditions for cognitive development for the student.