Increasing evidence indicates that individuals with Intellectual Disabilities (ID) might benefit from phonics-based reading instruction. However, research and instruction in this field has predominantly focused on sight word reading. Models for complex interventions recommend that feasibility research be conducted prior to conducting randomised studies to assess efficacy of interventions (Thabane et al., 2010). The aim of the current paper is therefore to investigate feasibility questions relating to conducting a full-scale randomised controlled trial (RCT) evaluation of an online, phonics-based reading programme (Headsprout™ Early Reading; HER) with children with ID. Employing a randomised pre-test post-test group design, this study explores and trials important aspects of a RCT evaluation to inform a full-scale RCT. We also found that HER had a significant effect on reading skills when compared with 'education as usual', with large effect sizes on the main outcome measure. This indicates that further, more robust evaluations using HER with children with ID are a worthwhile pursuit.