Ricken, G., Fritz, A., & Balzer, L. (2007, November). A Developmental Model as Basis for an Arithmetic Achievement Test for Children. Presentation at the 4th Nordic Research Conference on Special Needs Education in Mathematics, Vaasa, Finland. Ricken, G., Fritz, A. & Balzer, L. (2007, November). A Developmental Model as Basis for an Arithmetic Achievement Test for Children. Paper presented at the 4th Nordic Research Conference on Special Needs Education in Mathematics, Vaasa, Finland.