Fast mapping weaknesses in children with specific language impairment (SLI) may be explained by differences in disambiguation, mapping an unknown word to an unnamed object. The impact of language ability and linguistic stimulus on disambiguation was investigated. Sixteen children with SLI (8 preschool, 8 school-age) and sixteen typically developing age-matched children selected referents given familiar and unfamiliar object pairs in three ambiguous conditions: phonologically distinct word (PD), phonologically similar word (PS), no word (NW). Preschoolers with SLI did not disambiguate, unlike typically developing age-matched participants, who consistently selected unfamiliar objects given PD. School-age children with SLI disambiguated given PD. Delays in disambiguation for young children with SLI suggest limitations in processes that facilitate word learning for typically developing children. School-age children with SLI consistently selected familiar objects for PS, unlike typically developing children, suggesting differences in phonological activation for word learning.