Objective There is evidence that Cognitive Stimulation Therapy and maintenance Cognitive Stimulation Therapy are effective in mild to moderate dementia. There is, however, little evidence available for its implementation in practice and the impact of outreach support on the sustainability of the programme. Methods Two hundred and forty‐one staff members were randomised from 63 dementia care settings between outreach support including an online forum, email, and telephone support, compared to usual Cognitive Stimulation Therapy control group. The primary outcome was average number of attendees to the Cognitive Stimulation Therapy and maintenance Cognitive Stimulation Therapy programmes. Results There was no difference in average number of attendees between the intervention and usual Cognitive Stimulation Therapy control groups for the Cognitive Stimulation Therapy (p = 0.82) or the maintenance Cognitive Stimulation Therapy programme (p = 0.97). Conclusions Outreach support does not affect the average number of people with dementia attending the Cognitive Stimulation Therapy or maintenance Cognitive Stimulation Therapy programme. Irrespective of outreach support, the programmes remain widely implemented and yield perceived benefits for people with dementia. Copyright © 2017 John Wiley & Sons, Ltd.