They say teachers must have eyes on the back of their heads. This is definitely true on some level, and there are some very obvious, but not necessarily intuitive, tricks to get close to this reality--close enough that you might actually hear your students say, "What, do you have eyes on the back of your head or something?!" 

You can't really be in charge if you don't see what happens.  In our ideal classroom, we could probably turn our backs and business would continue as usual.  But, especially in the beginning, and especially with middle schoolers, this is pretty unrealistic.  It is key to figure out how to always keep your eyes on the class. 

Train yourself to move around the room so that you can see the entire class in your peripheral vision. This sometimes means not taking the most direct route to a student's table, but walking around all the desks to end up next to the student. If you sit down at a table with a group for a few minutes or a work period, it is worth making sure your seat is facing the rest of the class.  (Think of yourself as the gangster who insists on a seat in the restaurant where his back is to no one.)  I'll even ask a student to switch seats with me so I can have the one where I can see the class.  

In your front board/teaching space, try to have your handouts and the basic supplies you might need so you don’t have to walk to your desk or a closet during class to get something.  Have students pass things out while you watch.  When you circulate around the room, adjust your traffic pattern to maintain the most possible students in your line of vision.  

I'm sharing this because it's so obvious and easy to do, you might miss it.  I know I did, until somewhere in the middle of the year, I was helping students work in groups with my back to most of the class. Thankfully, my mentor pulled me aside and said, "You should try sitting over there."  She pointed to the space across from where I had been. "So you can watch the rest."  After that, I was always aware of my positioning. Sometimes, I get comfortable with a class and allow some blind spots.  That never lasts long, though.   

While kids don’t really know or appear to care that you’re walking the long way or are very particular about which seat ou sit in, they do notice when you don't keep watch. In fact, there are always a few students waiting for those very moments ;)  For their sake, and everyone else's, better to always be watching.