The impact of educational technology is a key question for both start-ups and traditional educational publishers. Teachers need to know, what a solution is teaching, why it is effective and how it can be used. The traditional educational material publishers have the advantage of having a long history of being used at schools and therefore plenty of practical experience on what works. However, gathering real evidence is a project that takes time and requires expertise. But when it's done properly the work pays off. Here I’d like to present some examples of how it can be done.