The last decades have seen increased emphasis on the quality of training for direct-care staff serving people with intellectual disabilities. Nevertheless, it is unclear what the key aspects of effective training are. Therefore, the aim of the present meta-analysis was to establish the ingredients (i.e., goals, format, and techniques) for staff training that are related to improvements of staff behaviour. Our literature search concentrated on studies that were published in a period of 20 years. Fifty-five studies met the criteria, resulting in 502 single-subject designs and 13 n>1 designs. Results revealed important information relevant to further improvement of clinical practice: (a) the combination of in-service with coaching-on-the-job is the most powerful format, (b) in in-service formats, one should use multiple techniques, and verbal feedback is particularly recommended, and (c) in coaching-on-the-job formats, verbal feedback should be part of the program, as well as praise and correction. To maximize effectiveness, program developers should carefully prepare training goals, training format, and training techniques, which will yield a profit for clinical practice.