Action research is a form of professional inquiry in which the teacher's role is seen as key to educational improvement. This paper describes methodologies developed by the Logo Action Research Collaborative - a national network linking 100 teachers at nine sites - that facilitate and support collaborative inquiry by teachers into their own teaching practices, in order to understand, improve, develop, and incorporate new forms of student assessment, teaching methods, and curriculum. The project focused on the Logo computer language, a powerful learning environment for problem-solving and mathematical inquiry. The authors provide background information on action research as an evolving discipline. They identify three phases of a year-long action research cycle, and describe key strategies developed by the project to support teachers in taking on a research frame of mind, identifying areas of concern, and undertaking and completing action research projects. The paper includes several illustrative examples of action research investigations undertaken by teachers, and demonstrates the benefits to the students and teachers involved. It closes by making a case for the potential contribution of action research to current educational reform initiatives and school restructuring.