Well, I don't teach primary so can only talk about y7 upwards but it sounds as if you need to think anout how you present yourself. It's no good saying something if you give the impression you don't mean it. Absolutely do not let them talk over you - you have to perform - give the 'look', scan the room, wait and then assert yourself in the silence. Insist on working in silence for however long is appropriate and then say something like, 'Now we're alll working nicely, you can talk to the person next to you about x and y.' As soon as the noise level goes up, warn and act. Set up activities where you can sit or stand somewhere and monitor the whole room. Stamp on the first child that tries to wander. Be friendly with individuals but firm with whole class. Try to convey confidence even if you don't have it - it takes a lot of energy to carry a class along with you. Personally, I find it easier when they're younger but that's not the case for everyone. And I'd lay off the telling them the rules. You probably only have half a dozen kids playing up although it feels like the whole class. And you will have nice children who want to please you so make a list and target them. Lots of attention. Focus also on a few sheep in the moddle that you can win round. Don't let it all be about the naughty children. Good luck!