The 19-year-old has signed a four-year contract with the Championship side.
Peterborough United manager Darren Ferguson told the club's official website: "We have been tracking him for quite a while as have a number of clubs and I like him a lot. He is a real athlete, can play in plenty of positions, is young and is willing to learn.
"He ticks a lot of the boxes, we have had a lot of good reports on him and I made the final decision after he played against us for Southend in the cup. He was their best player, I know we won the game comfortably (4-0), but he impressed me.
"He has got a lot of good attributes and I have a good chat with him. He will be a very good signing for us. He can play anywhere across midfield, he can play right back and can probably play at centre back.
"He is still developing, but for a 19-year-old he is a good size already. I am quite excited about this signing, I have to be honest," Ferguson said.