According to the AGREEMENT/TENSE (Agr/Tns) OMISSION MODEL, children's failure to produce finite verb morphemes represents the selection of an optional infinitive form, in which tense and/or agreement is not specified. When agreement is specified, nominative case is licensed. Following the assumptions of this model, a child's utterance such as She run reflects a failure to specify tense only, given that the subject pronoun shows nominative case. We tested this assumption in two studies through the analysis of spontaneous speech samples from young typically-developing (TD) children and children with specific language impairment (SLI). In Study 1, 15 children were included (TD aged 2;1–3;11, SLI aged 4;0–6;2); in Study 2, 33 children were included (TD aged 2;5–3;11, SLI aged 3;6–6;9). We determined whether there was a relationship between the children's use of past tense -ed and their use of third person singular -s and copula is when nominative case was also used. Because nominative case was used, any failures to produce third person singular -s and copula is should be attributable to tense and not agreement. Such use should therefore be related to the children's use of -ed which presumably hinges on tense only. However, a relationship was not found in the speech of either group of children. This was true both for the children in each group who were consistent in using nominative case pronouns and for those who were not. Possible reasons for these findings are discussed.