This systematic literature review addresses 20 years of intervention research conducted between 1990 and 2010 in which adults in any role serving preschoolers with or without delays or disabilities were taught skills applicable to children in classroom settings. Acceptable inter-observer agreement was reported for (a) the criteria for including research articles in this review and (b) the article content items. Review findings summarised the (a) characteristics of preschool staff, children, and settings, (b) professional development training topics and methods of training, and (c) research characteristics and findings. The 69 studies in this database lend credibility to the use of professional development to improve classroom-related skills in preschool teachers and staff. Most of these studies included professional development methods that have been identified as being indicators of effectiveness: modelling, demonstration by instructors, and feedback to participants both during workshops and classroom-based interventions. (author abstract)