Over more than a decade, specialist Applied Behavior Analysis (ABA) schools or classes for children with autism have developed in the UK and Ireland. However, very little is known internationally about how ABA is defined in practice in school settings, the characteristics of children supported in ABA school settings, and the staffing structures used. To answer these questions, the focus of the present research was a nationwide census of ABA schools throughout the UK. As far as it was possible to ascertain, we achieved a 100% return rate. There were 14 ABA schools and classes throughout the UK, supporting 258 children with autism, and employing 382 staff that supported ABA teaching. The mean ratio for ABA staff to children was 1.4 staff members: 1 child (range 0.7:1-2:1). The majority of all staff members were graduates or had a higher academic qualification (67.7%). This census methodology, if repeated, may help to identify future trends and can provide a baseline for developments in ABA schools/classes in the UK. (Contains 6 tables and 1 figure.)