Okay Dresden was what 16 when he killed his teacher? He hadnt lived with Justin but for a 3 or 4 years. Elaine came to leave them after Dresden had already been living there I believe. They are now in their 30s. That is a long time between the time when they were young and learning a little and the now. I am more than willing to say that Harry learned far more in the last 10 or 20 years after killing Justin than he did from Justin.