By the time David is sixteen, he has undergone a major change in thinking. Not only is he more sure of his views towards Waknuk society and its beliefs, he is more self aware of the dangers of being found out. He has matured greatly; his views are not influenced by his teachings, he has his own opinions.
The first time David's first "small doubts" started to emerge was after he met Sophie. Upon meeting her, she had seemed absolutely normal; even upon seeing her foot, his rote learned teachings did not come to mind; he simply felt sorry for Sophie. Upon being confronted by Sophie's mother, about the importance of keeping her secret to himself, he does not really understand the reason of the emphasis being put on keeping the secret. It is only after he sets off for home that he realizes that Sophie does not conform to the "true image", and is therefore classified as deviant.
David does not understand why a small toe should make a difference, and so continues his friendship with her.
They are very close; he picks a fight with the stronger Alan Ervin for her, and only gives away her secret after a huge beating. For him, it is not the beating that causes him so much pain, than the pain of self-contempt, of having given her secret away. He even tells the inspector a bit of what he thinks about Sophie being a mutant. Though David is not seen thinking about her later in life, his brief friendship with her has a huge impact on him. His conversation with the inspector is the first time his views have differed from those that he has been taught. Till the very end, he refuses to accept that Sophie is the work of...