doesn't sound to me like he's ready for K yet. I'd just let him enjoy another year at home and see if you can get him into a preschool or other group activity couple times a week. I would only put my child in K early if he really REALLY wanted to go to school and enjoy it there. Otherwise there's plenty of time to go next year.
Plus, the teacher knowing your son was admitted early probably expected him to know things like the whole alphabet (upper and lower case) and other basics since from what I understand, the kids that are admitted early are usually those who are way ahead (reading, doing math operations, etc.) ... they are usually entering K being on the 1st or 2nd grade level or even higher.
So, I'd just let him have fun, forget the flashcards, play games with him, or in my opinion even the right tv show will teach him more and will be more fun than flashcards. And give him a chance to be more emotionally ready for next year.
