Similarities and differences in L1 and L2 development. Opening up the perspective: incvluding SLI

By tradition, comparisons between first and second language acquisition involve data from child or adult L2 learners and data from young L1 children. However, there is a subgroup of L1 children, namely children with Specific Language Impairment (SLI), which is rarely accounted for in these comparisons. These are children with significant problems in acquiring their mother tongue despite growing up in a monolingual environment. In this paper, Processability Theory (Pienemann 1998) is used as a framework to compare the development of morphosyntax in three groups of children: L1 children, L2 children and children with SLI. Contrary to expectations, the results show that the development of grammar in children with SLI sometimes is more similar to the grammatical development in L2 acquisition than that in L1 acquisition. A similarity between these two groups has implications for theories about language acquisition and language impairment.