Background: The landmark findings of the Mother–Infant Transaction Program (MITP) showing improved neurodevelopment of preterm infants following parent-sensitivity training delivered in the neonatal intensive care unit have not been consistently replicated. This study evaluated an MITP-type intervention in terms of neurobehavioural development to preschool age. Methods: A randomised controlled trial involved 123 very preterm and extremely preterm infants allocated to either a parent-sensitivity intervention (PremieStart, n = 60) or to standard care (n = 63). When children were 2 and 4.5 years corrected age, parents completed the Child Behavior Checklist (CBCL). General development was assessed at 2 years with the Bayley Scales of Infant Development (Bayley-III). At 4.5 years, cognitive functioning was assessed with the Wechsler Preschool and Primary Scale of Intelligence (WPPSI-III) and executive functioning with the NEPSY-II. Results: There were no significant between-group differences in behaviour problems at 2 or 4.5 years, general development at 2 years, or cognitive and executive functioning at 4.5 years. Conclusion: Advances in the quality of neonatal intensive care may mean that MITP-type interventions now have limited additional impact on preterm infants’ long-term neurobehavioural outcomes. The gestational age of infants and the exact timing of intervention may also affect its efficacy.