The effectiveness of three types of in-service training designed to improve early intervention practitioners' abilities to use family-systems intervention practices was evaluated in the study of 473 participants. Participants attended either conference presentations or one of two types of workshops (half day/full day or multi-day), or received one of two types of on-site, field-based training (basic and enhanced). Study participants made self-ratings of the usefulness of the training content and the extent to which the trainings improved their abilities to work with families. The ratings were made either one month or six months after the trainings were completed. Results showed that both types of on-site, field-based training were associated with greater benefits compared with the other types of training, and that the enhanced field-based training was associated with optimal participant benefits. The key features of in-service training associated with positive learner benefits included active practitioner involvement in the learning opportunities (application, reflection, self-assessment, etc.), which occurred on multiple occasions over time. (Contains 3 tables and 3 figures.)