For much of the past two decades, expensive and often imported evidencebased programmes (EBPs) developed by clinician-researchers have been much in vogue in the family and parenting support field, as in many other areas of social provision. With their elaborate infrastructures, voluminous research bases and strict licensing criteria, they have seemed to offer certainty of success over less packaged, less well-evidenced locally developed approaches. Yet recently, evaluation research is showing that success is not assured. EBPs can and regularly do fail, at substantial cost to the public purse. In times of severe resource pressure, a pressing question is, therefore, whether lower cost, home-grown, practitioner-developed programmes-the sort often overlooked by policy-makers-can deliver socially significant and scientifically convincing outcomes at lower cost and at least on a par with their better resourced cousins. This paper shows how the application of techniques increasingly used in implementation science (the science of effective delivery) could help level the playing field. Processes for doing this including co-produced theory of change development and validation are illustrated with reference to the Family Links Ten Week Nurturing Programme (FLNP-10), a popular manualised group-based parenting support programme, designed and disseminated since the 1990s by a UK-based purveyor organisation. The paper draws out general principles for formulating and structuring strong theories of change for practice improvement projects. The work shows that novel application of implementation science-informed techniques can help home-grown programmes to compete scientifically by strengthening their design and delivery, and preparing the ground for better and fairer evaluation.