This systematic literature review presents a review of the effects of integrated language arts, science and technology (ILS&T) instruction, with an inquiry- or design-based pedagogy, in elementary schools on student achievement. To this end, an overview of the characteristics of the 19 included studies and their interventions is first presented. Second, the effects of interventions in relation to the study characteristics and outcome variables were examined, by comparing the mean effect sizes. The findings demonstrate positive effects of ILS&T instruction for all reported student learning outcome variables. Third, the relation between characteristics of the intervention and effect sizes was analysed. Interventions with higher levels of integration, a short duration, and teacher professional development activities produce higher effect sizes. These findings are relevant for the design of ILS&T interventions. The analysis was challenged by a lack of detailed information in study and intervention descriptions, which prompts a call for scholars to provide more comprehensive information in their intervention studies.