This quasi-experimental intervention study examines the effect of genre-based instructional practices on 90 primary students’ narrative writing achievements and is a result of six teachers’ action to meet the educational goals of the Swedish national curriculum. Specifically, the authors examine the effects of Joint Construction, the phase in the genre pedagogical model of the Sydney School known as the Teaching and Learning Cycle, in which teachers and students work together to co-construct texts. Joint Construction has been put forward as the most powerful part of the Teaching and Learning Cycle. The authors challenge this argument, presenting findings that are inconsistent with this widely held belief. Using a pretest-posttest control group design, the study shows that the Joint Construction stage did not significantly improve the quality of students’ narrative writing or increase the text length of their writings.