Flowers for Algernon

Charlie didn't tell his father who he was for a few reasons...... first, his father didn't recognize him, even after he asked him to look harder. Second, Charlie was no longer the boy he sent away..... the boy he sent away was a different Charlie that no longer existed.

How could I tell him? What was I supposed to say?
Here, look at me, I'm Charlie, the son you wrote off the books? Not that I blame you for it, but here I am, all fixed up better than ever. Test me. Ask me questions. I speak twenty languages, living and dead; I'm a mathematical whiz, and I'm writing a piano concerto that will make them remember me long after I'm gone.
How could I tell him?
How absurd I was sitting in his shop, waiting for him to pat me on the head and say, "Good boy." I wanted his approval, the old glow of satisfaction that came to his face when I learned to tie my own shoelaces and button my sweater. I had come here for that look in his face, but I knew I wouldn't get it.
"You want me to call a doctor?"
I wasn't his son. That was another Charlie. Intelligence and knowledge had changed me, and he would resent me-as the others from the bakery resented me-because my growth diminished him. I didn't want that.