A 10-year retrospective analysis was done using training records for 869 trainees who had attended a 40-hour course for hazardous waste site work. The course is intended for professional site workers, but had been attended by a demographically diverse audience. Analysis of test, demographic, and course data revealed some spurious effects but also indicated that trainees were not disadvantaged in their learning gains based on their own background or that of the class overall. Moreover, a large class appears to present some advantages, and a diverse class appears to present advantages in training material applied across work duties (hands-on skills, decontamination, etc.). Logistics encountered in the study raise doubts that a definition of professional/nonprofessional can be achieved or applied. Overall, the routine practice of providing separate training to professionals and nonprofessionals requires revisiting.