This site contains data, analysis code, and supporting materials for the following article: Crawford, M., Raheel, N., Korochkina, M., & Rastle, K. (2024). Inadequate foundational decoding skills constrain global literacy goals for pupils in low- and middle-income countries. *Nature Human Behaviour*. Learning to read is the most important outcome of primary education. However, despite substantial improvements in primary school enrolment, most students in low- and middle-income countries (LMICs) fail to learn to read by age 10. We report reading assessment data from over half a million LMIC pupils from 48 countries tested primarily in a language of instruction and show that these pupils are failing to acquire the most basic skills that contribute to reading comprehension. LMIC pupils across the first three instructional years are not acquiring the ability to decode printed words fluently, and in most cases, are failing to master the names and sounds associated with letters. Moreover, performance gaps against benchmarks widen with each instructional year. Literacy goals in LMICs will be reached only by ensuring focus on decoding skills in early grade readers. Effective literacy instruction will require rigorous systematic phonics programmes and assessments suitable for LMIC contexts.