Measuring the effect of training interventions is often demanded by organisations and commonly accepted by trainers. However, this is not the case with coaching. The result of individual coaching is often regarded as a private, internal process. Also it is influenced by many uncontrollable outside factors, that make it difficult to isolate what change occurred through coaching and what happened due to other influences. The question is also: when can coaching (as a long term intervention) be regarded successful? If one wanted to measure the effect of a coaching intervention, how would the design criteria for developing a measurement tool look like?