Cash, caveat, I'm not a parent, but bullying is one of my nasty sore spots. If bullies get away with it, it will just go on and on; bullies made my life hell in school right up through 7th grade, and it only stopped then because I changed schools. No adult ever intervened. Bullies don't grow up and stop, they don't stop until someone stops them.
I've been monitoring the situation. The thing that pissed me off was I SAW the kid mocking Owen today while I was volunteering in the classroom. When Owen said the kid said, "stupid stuff to him at recess" I told him we didn't talk about our friends that way. Owen said, "He's not my friend. He's mean to me." Then the kid gave us both this evil smirk and laughed. I told Owen that it doesn't matter what Tyler does, just what HE does and we don't treat people like that.
But in the first Open House we went to, Owen mentioned to me that Tyler called him an idiot on the playground, I've been keeping my eye on that kid. If he wants to make it to six, he'd better leave my kid alone.