Since 2003, the Essential Skills Series training program developed by the Canadian Evaluation Society has been offered to more than 15 groups in the province of Québec. The evaluations of these workshops were based on the participants' reactions collected by a Participant Feedback Questionnaire. This article describes the process used to assess the structure of the questionnaire and document its psychometric properties in order to determine whether it covered all subjects addressed by the training program and the extent to which it measured the items it was intended to measure. The results suggest that the questionnaire is effective in measuring participant responses to all the relevant components of the training program. This procedure may interest professional evaluators who want to ensure that questionnaires used to evaluate training programs are suitable for their intended purpose.