1. Introduction to the papers of TWG23: Implementation of research findings in mathematics education;Aguilar, M. S.
2. Boundary crossing and boundary objects;Akkerman, S. F.
3. Teachers investigate their work: An introduction to action research across the professions;Altrichter, H.
4. Dirichlet principle: Part I and II;Andžāns, A.
5. Summary tasks for central topics in the junior-high school curriculum;Arcavi, A.