The school is the finest school and seven years’ studying there should be great for students, but I can’t read it that way for some reason.
“If he wants ter go, a great Muggle like you won’t stop him,” growled Hagrid. “Stop Lily an’ James Potter’s son goin’ ter Hogwarts! Yer mad. His names’s been down ever since he was born. He’s off ter the finest school of witch craft and wizardry in the world. Seven years there and he won’t know himself. He’ll be with youngsters of his own sort, fer a change, an’ he’ll be under the greatest headmaster Hogwarts ever had, Albus Dumbled—“ (Harry Potter 1 [US Version]: p.58) [Bold font is mine]
If seven years there and he still doesn’t understand who he is, the school, I would think, is not so effective. The context is saying, however, the school is very good. Would you guide me to the right meaning?