Some children have particular difficulty comprehending written text: despite being able to read words quite well, they struggle to understand what they have read. So called “poor comprehenders” are not rare, with estimates varying between 5-10% of children in mid-childhood. There is now a large body of work documenting the nature of poor reading comprehension in mid-childhood and in particular, its association with spoken language abilities. However, we know relatively little about its precursors earlier in development, or its consequences for later childhood and beyond. The longitudinal data contained in ALSPAC will help us understand why it is that some children fail to comprehend, and what the consequences of this are for educational achievement and emotional well-being in the secondary school years and beyond. Our findings will help inform and specify educational interventions for children with poor reading comprehension.