The International Early Learning and Child Well-being Study (IELS) provides internationally comparable data on the early learning, development and well-being of five-year-old children.
This Technical Report documents the design, implementation and data processing procedures for the second cycle of IELS (IELS 2025). It provides a comprehensive account of the methodologies, standards and quality assurance processes used to support the transparency, reliability and international comparability of the study’s results.
The report covers all major phases of IELS 2025, including the development of assessments and questionnaires, sampling design, translation and linguistic quality verification, field operations, survey weighting, the scaling of cognitive and contextual measures, data management, data adjudication and the preparation of the international database. It also describes the procedures used to promote consistent implementation across participating jurisdictions and to ensure the quality of the data collected.
As the principal technical reference for IELS 2025, the report is intended for researchers, psychometricians, survey methodologists, policy analysts and other users of the study’s data products. It provides the methodological information needed to understand, interpret and use the international database, while documenting the rigorous processes that underpin robust international comparisons.
