The Kooikerhondje is an intelligent dog and they love nothing better than to please which in short means that in the right hands, they are highly trainable and they thoroughly enjoy the one-to-one attention they are given during training sessions. However, Kooikers need to be handled gently, yet firmly so they understand who is the alpha dog. It's important for these dogs to know who they can look to for direction and guidance or they might take on a more dominant role which can make them harder to handle. Like many other breeds, they are quite sensitive by nature and as such they do not respond well to any sort of harsh correction or heavier handed training methods. They do answer very well to positive reinforcement which always brings the best out of these clever dogs.
The key to successfully training a Kooiker is to make their training sessions as interesting as possible and to avoid too much repetition which can make it harder to keep a dog focussed on what they are being asked to do. Shorter more interesting training sessions tend to work a lot better than longer more repetitive ones when training a Kooikerhondje.