J. Child Lang.  (), –. Printed in the United Kingdom   Cambridge University Press The acquisition of past tense morphology in Icelandic and Norwegian children : an experimental study* HRAFNHILDUR RAGNARSDO  TTIR Iceland University of Education HANNE GRAM SIMONSEN University of Oslo  KIM PLUNKETT Oxford University (Received  January, . Revised  February, )  Icelandic and Norwegian past tense morphology contain strong patterns of inflection and two weak patterns of inflection. We report the results of an elicitation task that tests Icelandic and Norwegian children’s knowledge of the past tense forms of a representative sample of verbs. This cross-sectional study of four-, six- and eight-year-old Icelandic (n  ) and Norwegian (n  ) children systematically manipulates verb characteristics such as type frequency, token frequency and phonological coherence – factors that are generally considered to have an important impact on the acquisition of inflectional morphology in other languages. Our findings confirm that these factors play an important role in the acquisition of Icelandic and Norwegian. In addition, the results indicate that the predominant source of errors in children shifts during the later stages of development from one weak verb class to the other. We conclude that these findings are consistent with the view that exemplar-based learning, whereby patterns of categorization and generalization are driven by similarity to known forms, appropriately characterizes the acquisition of inflectional systems by Icelandic and Norwegian children. [*] This work was supported by NOS-H, The Icelandic Research Council, The Iceland University of Education Research Centre (Hrafnhildur Ragnarsdo  ttir), the Oceania Group, Department of Linguistics, University of Oslo (Hanne Gram Simonsen) and the Economic and Social Research Council, UK (Kim Plunkett). We wish to thank Kirsten Meyer Bjerkan, Heiru  n Kristja  nsdo  ttir and Helga Jo  nsdo  ttir for assistance in carrying out the testing, and Michael Thomas, Graham Schafer, and Amalia Bjo  rnsdo  ttir for carrying out the statistical analyses. We also thank two anonymous reviewers for their helpful commentaries on this research. Address for correspondence : Hrafnhildur Ragnarsdo  ttir, Iceland University of Education, Stakkahlı  ,  Reykjavı  k, Iceland. 