Children with specific language impairment (SLI) often have extraordinary difficulty in the use of tense and agreement morphemes. Because spontaneous speech samples may not provide a sufficient number of obligatory contexts for these morphemes, structured probe items are often employed. However, these usually emphasize actions that can be readily illustrated through drawings, which tend to have third person subjects. In this paper we describe a method that has been successful in creating obligatory contexts for a first person morpheme--auxiliary "am"--that until now has been assessed exclusively through spontaneous speech samples. Participants were 32 mainstream American English-speaking children comprising three diagnostic subgroups: children with SLI, typically developing age-matched peers, and younger typically developing peers matched for mean length of utterance (MLU). The children participated in a task in which they described their actions for an audience; these descriptions required the use of auxiliary am. The results revealed that the children with SLI used auxiliary am with significantly smaller percentages than both groups of typically developing children, a finding that is consistent with findings that employ other tense and agreement morphemes. Clinical applications of this method are discussed. (Contains 1 figure.)