This article reports on the evaluation of an interactive interviewer training system with a large, heterogeneous sample of investigative interviewers of children. The system, delivered predominantly through computer-assisted learning activities, focused on how to elicit important evidential details from child witnesses in a narrative format. Two studies are reported, each adopting a pre-versus posttraining design. Study 1 examined the effect of the training on trainees’ (N = 92) performance, using mock interviews where an actor played the role of the child in a highly controlled manner. Study 2 examined the effect of the training on field interviews (N = 156) conducted prior to and after the training. Five measures were analyzed: (a) proportion of interviewer question types, (b) proportion of desirable interviewer behaviors, (c) adherence to the interview protocol, (d) interview length, and (e) the quality of evidential information sought. Overall, the findings provide clear support for the utility of the training system. Irrespective of the type of interview or measure, adherence to best-practice interviewing increased from pre- to posttraining, with some evidence supporting sustained performance 12 months after there had been no intervening training or supervision. The implication is that there is now an evidence-based alternative to the traditional classroom-based training system for investigative interviewers. Suggestions for future research are also discussed.