Background: Morphosyntax has been well researched in specific language impairment (SLI) and there is general agreement that children with SLI have particular difficulties with tense-marking. Less well researched is the role that aspect plays in the difficulties found in tense-marking, especially as tense and aspect are often confounded in English. Initial investigation of the understanding of aspect in preschool children with SLI suggests that they are less sensitive to aspect and its interaction with tense than typically developing (TD) children. It is unclear, however, what is the developmental trajectory of their understanding of aspect and its interaction with tense and whether these difficulties are still found in older children and adolescents with SLI. Aims: To investigate comprehension of the grammatical aspect contrast between completed events using the simple past tense -ed/irregular (perfective grammatical aspect) and ongoing events using the past progressive (imperfective grammatical aspect). The role of lexical aspect was also investigated through the balanced use of verbs that were inherently telic (i.e. have a natural end-point) and verbs that required the addition of prepositional phrase for a telic interpretation when used in the perfective aspect condition. Methods & Procedures: A sentence-picture matching task was administered to 10 participants with SLI (aged 12;10-16;8 years) and 30 language ability matched TD children who were split into three groups (mean ages: 5;10, 7;4 and 9;2). Outcomes & Results: Adult-like performance was found by all groups on the perfective aspect condition, but only by the oldest group of TD children on the imperfective aspect condition. The performance of the group with SLI was consistent with their much younger language ability matched TD children in their understanding of the progressive -ing when used to describe ongoing events that have taken place in the past. The lexical aspect of the telicity of the verbs was not found to have any significant effect on performance. Conclusions & Implications: Although further investigation of the understanding of aspect (both comprehension and production) is needed, the results have implications for therapy. The past progressive -ing construction is important, particularly for providing context and background information in narratives, but it is not explicitly taught in schools. Therefore, some focus on the temporal nature of tense-marking in therapy may be beneficial to individuals with SLI in understanding the temporal nature of events and how aspect interacts with tense.