Constructive mathematics and teaching

Abstract: Constructivists (and intuitionists in general) asked what kind of mental construction is needed to convince ourselves (and others) that some mathematical statement is true. This question has a much more practical (and even cynical) counterpart: a student of a mathematics class wants to know what will the teacher accept as a correct solution of a homework problem. Here the logical structure of the claim is also very important, and we discuss several types of problems and their use in teaching mathematics.