A group of Finnish-speaking children with specific language impairment (N = 15, M age = 5 years, 2 months [5;2]), a group of same-age typically developing peers (N = 15, M age = 5;2), and a group of younger typically developing children (N = 15, M age = 3;8) were compared in their use of accusative, partitive, and genitive case noun suffixes. The children with specific language impairment were less accurate than both groups of typically developing children in case marking, suggesting that their difficulties with agreement extend to grammatical case. However, these children were also less accurate in making the phonological changes in the stem needed for suffixation. This second type of error suggests that problems in morphophonology may constitute a separate problem in Finnish specific language impairment.

Children with specific language impairment (SLI) vary widely in their ability to use tense/agreement inflections depending on the type of language being acquired, a fact that current accounts of SLI have tried to explain. Finnish provides an important test case for these accounts because: (1) verbs in the first and second person permit null subjects whereas verbs in the third person do not; and (2) tense and agreement inflections are agglutinating and thus one type of inflection can appear without the other. Probes were used to compare the verb inflection use of Finnish-speaking children with SLI, and both age-matched and younger typically developing children. The children with SLI were less accurate, and the pattern of their errors did not match predictions based on current accounts of SLI. It appears that children with SLI have difficulty learning complex verb inflection paradigms apart from any problem specific to tense and agreement.