Observational learning is a successful method for improving writing skills in various genres. We explore effects of a five lesson intervention series based on peer observation. Fifty-five Swedish 5th-grade students aged 10-12 years followed this intervention programme. The students watched short film clips with peers working with texts. Each lesson was organised according to a theme: reader's perception of the text, ordering of events, how to begin a story, how to end a story and how to edit a text. The students wrote four texts during the intervention. The quality of these texts was assessed by a panel of trained raters. Additionally, the language and reading comprehension and working memory capacity were tested. The results show that average text quality had significantly improved at the end of the intervention, and that this improvement was modulated by reading and language comprehension. Three months later, however, text quality was significantly decreased.