It is a well-known phenomenon in educational research and policy. An educational intervention works brilliantly in ten schools. Teachers are enthusiastic, the results are promising, and researchers report a positive effect. The next step seems obvious: roll it out to a hundred or even a thousand schools. Perhaps even make it the norm.

And that is often where things go wrong.

Researchers even have a name for it: the scale-up effect. Interventions that perform well in small-scale studies often lose part of their impact when they are introduced on a much larger scale. That does not necessarily mean the intervention itself has become worse. Rather, the context has changed. More schools mean more teachers, more school leaders, more pupils, more local variation, and many more practical challenges. It sounds rather discouraging. Especially if it seems we can do nothing about it.

A new systematic mapping review by Rosanna Lea and colleagues therefore asked a different question from the usual What works? Instead of looking for the most effective intervention, the researchers analysed 79 educational interventions that had been successfully scaled up and examined how that scaling had been organised in practice. Their aim was not to identify a single golden formula but to map the building blocks that recurred.

So what did they find?

Virtually every intervention started with high-quality professional development. Most explained not only what the intervention involved, but also included demonstrations and opportunities for teachers to practise. One finding stood out: relatively few programmes gave participants the opportunity to exchange experiences with colleagues during the training itself.

Almost all projects also invested in high-quality materials, including detailed manuals, teaching resources, and practical tools. Coaching and other forms of ongoing support during implementation were also common. In other words, the researchers rarely assumed that a single training session would be enough. That fits well with what we already know about effective professional development.

Perhaps even more interesting is what appeared relatively rarely. Only a small proportion of the interventions explicitly invested in professional learning communities (PLCs), collaboration between schools, or fostering a sense of ownership among teachers. Yet these are precisely the elements that are often assumed to be essential for embedding educational innovations over the long term.

That does not mean PLCs are unimportant. The authors are careful to point out that this review is not a manual for successful implementation. They documented what researchers actually did when scaling interventions, not which individual components caused the interventions to succeed. Answering that question will require further research.

Even so, the review provides a remarkably useful checklist for anyone involved in improving education. If you want to scale up a promising intervention, do not focus solely on the intervention itself. Think just as carefully about professional development, teaching materials, implementation support, and how schools can sustain the change once the project team has moved on.

After all, a successful pilot is not yet a successful educational innovation.