...I did t even have to to out him on a circle and was still leading him in the arena when all of a sudden he went bronc on me, straight up and then started spinning! I have had him almost four months now, he came to me with the reputation of being a "skitzo" horse just throwing anyone who got him....in the almost four months I have had him he never has acted up, he went from pretty forward and spooky and up tight to acting like a school horse...These weren't little rears either full on straight up and coming back down and crow hoping to a spin to go up again...I had no clue to what it was he really reacted to and with him being so young and green...
Either the description you gave is inaccurate, or you have a horse that many would not consider suitable for a 3 year old.
Since you don't know what spun him up, how do you know he wouldn't go "skitzo" with the 3 year old? If he had behaved for 4 months and then freaked, why would an hour of good behavior convince you he was bombproof?