I'd go with 1st grade. DS had a fantastic pre-k teacher who let DS work at this own pace. After starting the K year full of enthusiasm at our local public school, he quickly got bored and frustrated. We had a long spell in Jan/Feb where he didn't want to go to school because he wasn't learning anything. He kept asking to stay home and saying that school was a waste of time since he'd learned all of this stuff last year.