Child sex trafficking (CST) is a worldwide public health and social justice issue. Evaluations of prevention program effectiveness have been limited by the lack of validated measures to assess CST-related constructs. We drew from theory to adapt measures of adult sex trafficking and intimate partner violence precursors or risk factors to develop measures assessing CST constructs including CST myths, self-confidence to address CST, and comfort in asking and reporting students among middle school staff. The two measures that were validated (CST myths and self-confidence) can be used to evaluate the effectiveness of CST prevention programs. Reducing the prevalence of CST is an essential component of promoting gender equality.