My September born 5 y.o, who is now in 1st grade, is a perfectionist. He quit piano because "I was not doing a good job playing the piano." even though his piano teacher said he was doing amazing for a 5 y.o. He learned to ride a 2 wheel bike by himself. He pretty much leaned to read by himself, with some help from Starfall and overhearing me teach my 7 y.o. He is VERY competitive. Everything must be as he expects it, or else he will not participate. And he must always win.

A generally well behaved kid, his behavior took a turn for worse after he started school and skipped K after a month.
I think his gifted, but not sure what level. I have a feeling he thinks he is very smart.

How do I handle his behavior, esp. getting frustrated when things don't go his way?