This paper compares the development of tense morphology and verb-second in different learner populations. Three groups of Swedish pre-school children are investigated longitudinally; ten L1 children, ten L2 children and ten children diagnosed with Specific Language Impairment (SLI). Data was collected twice, with an interval of six months. The results at Time I reveal a significant difference between normally developing L1 children on the one hand and L2 children and children with SLI on the other. The L1 children use verb-second correctly in topicalized declaratives, whereas both L2 children and children with SLI use structures with the verb in third position (XSV structures) as an intermediate step towards verb-second. There is a clear development between the two data collection sessions for the L2 children and the children with SLI, diminishing the difference between them and the unimpaired L1 children. The similarity that is found between L2 children and children with SLI in this study bears important implications for the discussion of the role of transfer in L2 research and for the question of a defective linguistic representation in SLI research.