Background: Shared reading interventions can impact positively on preschool children's language development and on their caregiver's attitudes/behaviours towards reading. However, a number of barriers may discourage families from engaging with these interventions, particularly families from lower socio-economic status (SES) backgrounds. We investigated how families from such backgrounds responded to an intervention designed explicitly to overcome these barriers. Methods: In a preregistered cluster randomised controlled trial, 85 lower SES families and their 3-year-old to 4-year-old children from 10 different preschools were randomly allocated to take part in The Reader's Shared Reading programme (intervention) or an existing 'Story Time' group at a library (control) once a week for 8 weeks. Three outcome measures were assessed at baseline and post intervention: (1) attendance, (2) enjoyment of the reading groups and (3) caregivers' knowledge of, attitudes and behaviours towards reading. A fourth -- children's vocabulary -- was assessed at baseline and 4 weeks post intervention. Results: Families were significantly more likely to attend the intervention group and rated it more favourably, compared with the control group. However, there were no significant effects on caregivers' knowledge, attitudes and behaviours or on children's language. Conclusion: The intervention was only successful in engaging families from disadvantaged backgrounds in shared reading. Implications for the use, duration and intensity of shared reading interventions are discussed.