Hi Cathy
((Hugs)) that is so sad! I can't believe that anyone would lose perspective to the point where they think that 'graduation' from Kindergarden is a proud accomplishment. I'll bet the part about 'and everyone else things so too' is a total fabrication. And the idea that your son would 'achieve' the honor of graduation through cheating: Bizzare! Anyway -
Here are the options:
A pretend that the letter was never recieved and that you just happened to be busy the day of graduation. In future if any such stuff comes your way, respond: "I know that a fellow as caring and sensitive as yourself will understand will understand that every child deserves to learn where they learn best, and for my son, at this moment, that is in your son's class. Practice in front of a mirror and with friends until you can do this smoothly.
B show the school staff. likely they will tell you that the fellow is odd and acts like this all over the place
C have a backup plan, keep your eyes out for a new school, or a new grade, etc.
D get friendly a few of the nicer parents at the school, who can do your PR for you. Obviously this fellow cares about 'what everyone else' is saying.
E Journal about what this reminds you of in your own growing up experience. Almost everyone has an older sibling, cousin or an aquaintance who tried to exclude them on some pretext at some point in their life. The key confusion towards children is a disrespect that comes at them from the adult world, and in then re-broadcast from one child to another. Children are given to understand that 'little' is bad and powerless, and that if they cooperate and wait, someday they will be the 'big' one who is good and important. DS11 was talking about it the other day in terms of all the pep talks the teachers at school gave about the glories of life in the upper grades.
((Hugs)) I'm so sorry that you got that weird letter!
Grinity