Collaborative writing (CW) has been proven advantageous to enhance the second and foreign language skills of university students. However, little research to date has explored whether CW practices are fruitful for secondary school learners in foreign language (FL) contexts, a population characterized by low language proficiency levels, and few opportunities to engage with the FL. The present classroom-based study examines CW in this setting and aims to determine whether CW fosters language opportunities, operationalized as language-related episodes (LREs), which will allow learners in low-input scenarios to compose better texts. Two parallel intact classes were studied: a control group (n = 16) which produced an argumentative essay individually, and an experimental group (n = 16) which did so in pairs while recording their interactions. The findings revealed that the pairs produced shorter but more accurate and slightly more lexically and grammatically complex texts and obtained higher scores in content, structure and organization. Collaboration afforded students the opportunity to pool ideas, deliberate over language use, and provide each other with feedback (collective scaffolding). Most importantly, collaborating seemed to be beneficial for all intermediate secondary learners and, thus, a useful strategy for improving FL writing skills in the secondary school context.