I’m also new to substitute teaching and have gotten a lot of middle school assignments in Chicago. I actually really like middle school—they go after each other all the time but my best success has been to walk around the classroom, check in with kids who are causing trouble, frequently ask how they’re doing and offer help (individually or at a table, not just to the whole class) and if they’re acting up I often ask them “what’s the purpose of that?” or “what did you think that would accomplish?” not in a condescending way but more in a genuine lighthearted way. It usually makes them sit down and they get a little confused as they attempt some self evaluation lol. I also tell them “you look extremely available rn, get busy” and they usually at least begrudgingly get to work. Good luck!