Parent training is proposed as an evidenced-based treatment for ADHD in preschool. This is important because parents and clinicians alike often feel uncomfortable about using medication for children under 6 years of age. However, many questions remain regarding the specifics of the costs and benefits of parent training in this age group. What outcomes does it actually improve? Which types of parenting training are most valuable for preschoolers? Does it have any negative effects? In this talk I will describe data from two recent large head-to-head trials to address these sorts of questions. The trials contrast the New Forest Parent Training Programme (NFPP), developed specially for parents of preschool children with ADHD and delivered one-to-one in the home, with two more generic behavioural approaches developed for children with conduct problems more generally but recommended for ADHD (“Helping the Non-compliant Child” and “Incredible Years”). The trials support the value of parent training for preschool ADHD – showing that non-specialist and group-based approaches are, in general, as good as NFPP. However, they also support the findings of recent meta-analyses that the effects of parent training on ADHD symptoms are limited to parent-rated non-blinded measures – raising doubts about whether they actually reduce ADHD symptoms or just change parents perceptions.