Long-Term Effects of Science Teacher Professional Learning Communities on Instructional Quality and Student Outcomes in Lagos State: A Four-Year Study

This study investigated the long-term effects of Science Teacher Professional Learning Communities on instructional quality and student science outcomes in Lagos State, Nigeria, through a four-year longitudinal study. Rigorous long-term evidence on Professional Learning Community effects in the Nigerian context is absent from the science education literature. A longitudinal quasi-experimental design was employed. Sixty secondary schools in Lagos State were assigned to either active PLC implementation or control conditions over four academic years. Science teachers in PLC schools participated in structured monthly collaborative inquiry cycles. Classroom observation protocols and student achievement data were collected annually. Mixed-model ANOVA and growth curve analysis were used to track trajectories over time. Results showed that schools in the PLC condition demonstrated progressively improving instructional quality scores and student achievement, with the rate of improvement accelerating from year two onward. Control schools showed minimal change. The cumulative effect size by year four was large, establishing practical significance. Qualitative case studies of high-growth PLC schools identified peer accountability, focused inquiry problems, and administrative backing as enabling conditions. The study makes a longitudinal contribution to the evidence base on PLCs in Nigerian science education and recommends systematic state-level PLC implementation with fidelity monitoring. Keywords: professional learning communities, Science teachers, longitudinal study, Lagos State, instructional quality.