The revised new forest parenting programme (NFPP) is an 8-week psychological intervention designed to treat ADHD in preschool children by targeting, amongst other things, both underlying impairments in self-regulation and the quality of mother–child interactions. Forty-one children were randomized to either the revised NFPP or treatment as usual conditions. Outcomes were ADHD and ODD symptoms measured using questionnaires and direct observation, mothers’ mental health and the quality of mother–child interactions. Effects of the revised NFPP on ADHD symptoms were large (effect size >1) and significant and effects persisted for 9 weeks post-intervention. Effects on ODD symptoms were less marked. There were no improvements in maternal mental health or parenting behavior during mother–child interaction although there was a drop in mothers’ negative and an increase in their positive comments during a 5-min speech sample. The small-scale trial, although limited in power and generalizability, provides support for the efficacy of the revised NFPP. The findings need to be replicated in a larger more diverse sample