How many learners in a class are said to be many? How might a Tanznian class with eighty learners affect the possibilities for good teaching and learning? How are teachers in crowded classrooms coping with a lack of teaching material, particularly textbooks? The study focuses on these kinds of questions by investigating Tanzania primary school teachers' experiences of prevailing teaching constaints and actions taken for improving classroom work. The results indicate a wide range of constraints and restrictions that hamper quality teaching. The results also reveal that firm actions for professional development can contribute to concrete improvements regardless of overfull classes and scarce teaching material. Thrugh a long lasting in-service program, teachers were trained to handle the prevailing conditions; for instance, to pay more attention to the individual learner, to increase cooperation with collagues and to utilize the environment as a teaching resource.