Now I know teachers who swear by not having seating charts, but the few times I've dipped my toe in those shark waters, I deeply regretted it. Therefore, in my experience, this is:
Mistake #3 - Not Having a Seating Chart.
I know that making seating charts is a lot of work, and it's a hassle to enforce them. But the difference between managing a class in which I have chosen everyone's seat up front and managing a class where they sit wherever they want to is night and day. Dark and Light. Demons and Angels. Hell and Heaven, or as close to classroom management "heaven" as I can get anyway.
If you let them sit wherever they want, you inevitably have to move some talkative, off-task students around anyway, and when you do that you have to argue and listen to whining and get the eye-rolls and sullen behavior just like you do sometimes when enforcing your seating chart. So just front load that eye-rolling session with a seating chart that's ready to go the first day of class. You'll get your turf established right away, and it's much harder for them to fight against it later since your class was clearly established like that, from the get-go.
Also, talk about the seating chart in your rules and expectations on your syllabus, or if you don't like having a lot of written rules (some teachers don't,) at least talk about it while you're going over the syllabus the first day of class. I say things like, "I organize my classroom with a seating chart that I design. I do this because [telling them why up front, because they are the "WHY" generation and that's how they get a little more buy-in,] I want to choose your partners rather than having you just sit by your friends, and leave some kids out. That way everyone meets new people, works with different people throughout the year, and my class runs smoother so I can teach you more Spanish. I expect you to sit in your assigned seat, without arguing or complaining about it, when the bell rings. If you have a problem with your seat, like you can't see the board or something, talk to me about it after class."
Here are my tips for creating good seating charts:
1. Space out the boys. You can do this whether you know the students or not. In Spanish, you'll get some really boy-heavy classes at times, so it's not an exact science, but in general, you want to make your grids boy-girl-boy-girl. I try not to have two boys next to one another either side-to-side or front-to-back.
2. Rowdy boys are in front. I call these the "power seats." Meaning, I have a little more (illusory) power over a loud, rambunctious kid if he's within a few feet of me. I can talk with him, joke with him, and ask him to settle down when needed, sometimes without most of the class even noticing that he and I have an exchange going. He naturally gets more attention from me, which is sometimes all that kid is looking for in the first place.
3. Quiet girls form a padding around rowdy boys. Sorry, quiet girls. Actually, sometimes they really enjoy this, because being partners with an outgoing, energetic guy brings her out of her shell a little, gets her laughing. Or, sometimes he drives her nuts. If I see that, I'll discreetly change that arrangement with my next seating chart.
I make new seating charts at the start of the semester, and I change them mid-semester. So that's four charts per class per year. Changing at mid-semester quells some of the complaining about having a seating chart, so to me, it's worth the extra work.
Also, you will have many students who really like having assigned seats, having a seat that is always theirs in my class that others can't just take whenever they want to, forming clumps of "cool" kids in certain areas of the room while the "outcasts" sit in the front, back, or whatever areas aren't "cool."
To sum up, I'd say making and enforcing seating charts is one of the top priorities in my own classroom management practice. It makes a world of difference for me, but I'd be curious to know what others think, so comment below with your thoughts!