This mixed methods study investigated the effectiveness and social validity of a teacher-implemented story writing intervention in a primary school in Aotearoa/New Zealand. A quasi-experiment indicated students who received the intervention showed higher gains in holistic quality, number and quality of story elements, and total words written compared to students who received their regular instruction. In an interview, the teacher indicated the intervention was appropriate to meet the needs of the students, had acceptable procedures, and meaningful outcomes. Thus, the quantitative and qualitative data converged to indicate the intervention was effective and had social validity.(c) 2022 Elsevier Ltd. All rights reserved.