"What doesn't kill you makes you stronger", but fuck it, not when you're an 8 year old.

I'm imagining now your ammunition magazine and one bullet of a larger caliber with the name of that professor carved on it 🙂

I had a similar situation with my handwriting, I endured criticism, but without punishment (physical punishment).
I was in third grade, 10 years old, when I started writing in tiny handwriting. While my school friends still wrote in those large and very understandable letters, I "reduced" my letters at least twice. It was still very understandable, precise and neat (on the line), but small, by my professor's standard.
I endured a short period of his criticism, he demanded that I go back to writing bigger letters, but I, like you, was stubborn (with the exception that it didn't hurt me - my father wrote in a similar handwriting and he didn't see what the professor asked me to be a problem, so he didn't punish me).
Some of my friends liked my new writing style, so they started to follow my example. So in the end the professor lost the battle 🙂
That reduction of letters in the handwriting later led to the doctor's style, so today even my handwritten signature is impossible to read. But, as the forensic experts told me, just like that (even worse than hieroglyphs), my personal and recognizable one, has its own seal.