A systematic review of professional development studies addressing multilingual learners in K‐12 STEM and humanities classrooms

Previous research shows K‐12 teachers are often insufficiently prepared to teach multilinguals (MLs), contributing to low educational attainments among this population. This highlights the need to review empirical studies on professional development (PD) programmes that address MLs' learning needs. Although several systematic reviews have examined PD, none have specifically focused on instructional practices in content‐area classrooms in ML‐focused PD studies and the outcomes associated with such PD. To address this gap, this study answered what teaching practices were implemented in K‐12 STEM and humanities classrooms in past ML‐focused PD studies and what teacher and student outcomes were examined in these studies. A total of 3253 articles were screened for eligibility, of which 48 met the inclusion criteria. Eligible articles were thematically analysed for teaching practices and outcomes of teachers and students. Findings indicated that PD programmes improved teacher outcomes (instruction, knowledge, attitudes and perceptions, self‐efficacy and confidence) and student outcomes (school achievement). Across studies, teachers were trained in eight key instructional practices (culturally and linguistically responsive teaching, language and literacy development, schema, scaffolding, explicit instruction, strategies, collaborative learning, assessment), implemented in both humanities and STEM classrooms. Two additional teaching practices (inquiry‐based teaching, 5‐E teaching) were used specifically in STEM classrooms. Findings suggest that content area teaching should be integrated with language and literacy instruction in classrooms with MLs. Further, future PD research may more explicitly design and examine assessment practices, suggesting a potential PD design gap, alongside limited attention to grades 6–12 and social studies educators. Context and implications Rationale for the study: Despite increasing student diversity, multilingual learners (MLs) continue to face achievement gaps, partly due to educators' limited preparation. Reviewing studies on professional development (PD) addressing MLs' needs is therefore essential. Findings from this study clarify how PD equips K‐12 teachers to support MLs' success in STEM and humanities classrooms. Why the new findings matter: These findings contribute to ongoing efforts to strengthen research, policy and practice related to PD for educators of MLs. By demonstrating the value of sustained, context‐responsive PD, they can inform the design of initiatives that better prepare educators to address the diverse linguistic, cultural and academic needs of MLs. Ultimately, strengthening such PD systems has the potential to enhance instructional quality and promote more equitable educational opportunities for MLs across K‐12 settings. Implications: At the practice level, effective ML‐focused PD requires feasible instructional strategies, administrative support, strong school–family communication and attention to disciplinary differences, ensuring implementation across grade levels and subjects. At the research level, PD outcomes should be interpreted within contextual factors, such as implementation fidelity, teacher attitudes and policy conditions to produce more credible conclusions. At the policy level, differentiated PD frameworks should recognize shared and discipline‐specific practices, promote cross‐disciplinary collaboration and align language, literacy and content learning goals. Policies should allocate sufficient time and resources to sustain effective PD implementation and support MLs' academic success.