After one year we already notice the effect since we often go somewhere and Kabouter exclaims to see so or so from school. The same thing happened recently when we went for a short "bike ride" in the neighbourhood park. One of the girls from his class was playing there and it was fun to see the interaction of the 2 kids and to see both of them race on their running bikes.
In the mean time Beertje sled from a slide for the first time and he loved it. Before we knew it this little dare devil simply launched himself down...quite a difference with his brother who didn't do it yet last summer!