There is, obviously, a measure of personal preference to your question. To some readers, an author's methods of character development may seem more effective and believable than to other readers. However, there is quite a bit of evidence from The Magician's Nephew that speaks of Lewis's adept skill for characterization.
Perhaps the best example of character development is through the main character, Digory, who grows up to become the professor in The Lion, the Witch, and the Wardrobe. Digory is first described as a sad and lonely boy who is struggling with the dire illness of his mother. Lewis describes him in chapter 1 as looking "like a boy who was so miserable that he didn't care who knew he had been crying." Yet, when he befriends his neighbor, Polly, Digory's life becomes brighter and more hopeful. Along with Polly, Digory is confronted by his Uncle Andrew, who tinkers with magic, and the two are sent to another world as an "experiment."
In this new world, Digory is curious to the point of recklessness. There is a sign that clearly states that danger will befall them in this new world if they ring a bell, yet Digory does it, despite Polly's warnings. This choice unleashes the villain of the story, Jadis, and shows another facet of Digory's personality that was yet to be seen. However, Digory grows at the end of the novel when he is confronted by Jadis again and is offered the chance to save his mother, whom he dearly loves. Yet, because of his growth as a character and his meeting with Aslan, Digory refuses.