The impact of educational technology is a key question for both start-ups and traditional educational publishers when looking at how to sell to schools. Teachers need to know, what the learning 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.