Successful education requires that the teacher has two knowledge competencies. The teacher not only needs to be familiar with the subject knowledge, it is also essential that the teacher have a realistic, detailed and practical knowledge of the students' understanding of the subject. This second kind of knowledge concerns the students' typical understanding and misunderstanding of the subject, and ways to handle them. It also includes ways to communicate meaning and interest in the subject--not to idealized students, but to real students. This paper describes a Swedish project that opens a channel allowing a teacher to systematically develop this knowledge while helping students. Teacher-student dialogues are conducted through a web page. As a result of the underlying goal, the project also extends the students' role in their education to a more responsible one. The textbook author uses the students' opinions and work at the web page to improve the book for the benefit of future students. Thus, the textbook evolves to be better adapted to the environment for which it is intended: studies by students. We present empiric results for an undergraduate distance course in calculus with 20 students.