Purpose: Phonological-semantic intervention has been shown to be effective in enhancing the vocabulary skills of children with language disorder in small-group or individual settings. Less is known about vocabulary interventions for adolescents with language disorder in whole-class models of delivery. The current study investigated the effectiveness of phonological-semantic vocabulary intervention for adolescents with language disorder, delivered by secondary school teachers within science lessons. Method: Seventy-eight adolescents with language disorder, aged 11-14 years, were taught science curriculum words by teachers in class, under 2 conditions: (a) 10 words taught through usual teaching practice and (b) 10 matched words taught using an experimental intervention known as Word Discovery, which embedded phonological-semantic activities into the teaching of the syllabus. Ten similar control words received no intervention. Word knowledge was assessed pre-intervention, postintervention, and follow-up. Results: At pre-intervention, measures of depth of word knowledge and expressive word use did not differ between usual teaching practice and experimental words. At postintervention, depth of knowledge of experimental words was significantly greater than that of usual teaching practice words. This significant advantage was not maintained at follow-up, although depth of knowledge for experimental words remained significantly higher at follow-up than at pre-intervention. At postintervention, expressive use of experimental words was significantly greater than that of usual teaching practice words, and this significant difference was maintained at follow-up. There was no change in students' depth of knowledge or expressive use of no-intervention words over time, confirming that the findings were not due to maturity or practice effects. Conclusion: The experimental intervention was more effective than usual teaching practice in increasing the word knowledge of participants. Clinical and teaching implications include the importance of intervening during the adolescent years, with classroom vocabulary intervention being a viable option for collaborative teacher and speech and language therapy/pathology practice.