Background: Children with language impairment show academic outcomes that are consistently poorer than those of their typically developing peers. A contributor to this is difficulty with reading comprehension. Although these difficulties are reported to continue well into adolescence, this population is generally underserved with regard to therapy. The efficacy of interventions for reading comprehension is well established in the research literature, but whether the same effects are achievable within a reasonable time reflecting available resources in real-life circumstances is less clear. Aims: Efficacy trials may significantly overestimate how strong an effect will be when the treatment is used under more natural conditions and within local constraints. The aim was to discover whether a short classroom intervention would be effective in improving reading comprehension in adolescents with the heterogeneous profiles of general or specific learning disabilities, additional diagnoses and behavioural and socio-emotional problems found in mainstream schools today. Method & Procedures: Twenty-eight adolescents with heterogeneous language and reading profiles were recruited from a mainstream school. The intervention programme comprised eight sessions of instruction in multiple reading comprehension strategies, held over 4 weeks. Experiment 1 had 10 participants. Experiment 2 had 18 participants who underwent the same programme, plus the addition of a session dedicated to decoding skills. Efficacy was evaluated within a pre- and post-study design, with baseline and post-therapy measures taken using the York Assessment of Reading for Comprehension (YARC). Outcomes & Results: Both experiments showed a significant group difference pre/post-intervention, with similar large effect sizes. Experiment 2 also showed a significant group difference in decoding ability pre and post the single intervention session. Conclusions & Implications: This short intervention programme proved effective in a population with heterogeneous profiles, and fitted well with delivery in a mainstream school setting. It showed significant gains can be attained for this client group with relatively few resources.