In this study interactive teaching of two math teachers at elementary schools in Spain was observed. Focus was on the description of the principles of the practice which guide the teaching activities of the subjects, because it was felt these principles form the base of teachers' theories with respect to the teaching and the students. During a 4-month period each teacher was observed once a week for an hour. The teachers were asked to keep a journal during the investigation. Lastly, teachers were interviewed on various occasions. The analysis of data is done by qualitative case studies. It was found that the teachers in this study used the following principles of the practice: compensation, supression of emotions, indulgence, progressive checking, authenticity, individualized attention, and intrinsic motivation. (Author/DF)