Ensuring the fidelity of programme delivery within efficacy trials is essential for accurate findings’ interpretation. The goal was to document the extent to which the How-to Parenting Program was delivered with fidelity during an efficacy trial. The five components of fidelity were assessed when this programme was delivered to parents in the experimental condition of a wait-list randomized controlled trial conducted in grade schools. The adherence of cofacilitators to the programme material was also elevated. Exposure was also elevated, with a majority of parents attending six or all of the seven 2.5-hr sessions and doing at least some of the recommended readings. Regarding delivery quality, parents rated cofacilitators as highly empathic, enthusiastic, and prepared. Parents appeared very responsive to the programme, as cofacilitators rated them as generally highly engaged, and the dropout rate was minimal. Regarding differentiation, rates of psychosocial services use were similar across conditions, but some parents on the wait-list read the How-to book. Apart from imperfect differentiation, the How-to Parenting Program was delivered with high fidelity during this trial. (PsycInfo Database Record (c) 2025 APA, all rights reserved)