Objective: Pain is common and complex for children with intellectual and developmental disabilities (I/DD). Secondary caregivers such as respite workers are lacking important pain-related information which can impact care. Here, we outline a randomized controlled trial (RCT) protocol testing the effectiveness of a pain training for respite workers supporting children with I/DD. Methods/design: Organizations enrolled in the RCT were randomly assigned to receive a 3-3.5 hours pain or family-centered care training. Data were collected immediately before, after, and 4-6 weeks following completion of the training. Outcomes are as follows: pain knowledge (primary), pain assessment and management perceptions (secondary), training evaluations (secondary), and use of pain assessment and management skills (tertiary). Both quantitative and qualitative methodologies are being used including questionnaires, rating scales, a standardized vignette, and focus groups. Conclusions: Results from this trial will be used to further understand the impact of the pain training and inform next steps related to implementation. TRIAL REGISTRATION: ClinicalTrials.gov identifier: NCT03421795.