It's "Zac" not "Zach" or "Zack" or "Zachary"

Two weeks ago when I was looking through Zachary's Thursday take home folder from PreK I noticed he wrote "Zac" and some random letters on the top of one of his assignments. I asked him what it said and he responded "Zac, Z - A - C, that's how you spell my name, I don't want it longer any more." I asked him why and he said he didn't know but he liked "Zac". So I asked if he wanted it spelled "Zach" (which is what I had planned from the day we decided his name would be Zachary) and he said no that he did not want the "h" on his name. I made sure he understood that he still needed to practice his whole name sometimes but that if he wanted to be called Zac and spell it that way it was his choice which made him happy so we told his teacher who was more than willing to accommodate Zac but she forgot one day and wrote Zachary on something and Zac was quick to point it out that she spelled his name wrong. So Zachary is now Zac...just so ya know.