The CSL study assesses the primary schooling system in Ireland, aiming to understand children's learning, engagement and well-being. CSL includes approximately 4,000 participants in two cohorts. In each cohort, a representative sample of schools was recruited to reflect the population of primary schools nationally, reflecting key characteristics (school size, gender mix and disadvantaged status). Cohort A consists of children aged 4 to 5 years from 87 schools, and Cohort B includes 8 to 9-year-olds from 102 schools. This study additionally involves the participation of parents, class teachers and school principals, alongside in-depth case studies of 13 of the schools. Follow-ups are conducted annually, with waves of data occurring between 2019 and 2023. CSL follows Cohort A from primary school until 2nd class (age 8-9 years) and Cohort B from 2nd class through to the end of primary school (12-13 years).