And there is a gulf a mile wide between being sworn at and somebody swearing in your presence. If it's just come out because they weren't thinking and used their everyday language, a 'look' and 'different words, please, Michael' usually gets an 'Oh, shit, I'm sorry Miss'. (Facepalms are a legitimate means of communication). If they're upset, frustrated and angry, just don't hear the swearing and ask 'How can I help?'.
You're the grown up. You're supposed to be in control - of yourself, first and foremost. The screeching, bellowing and raging is either funny if they are in a group large enough to know they're safe, but a fuckton of those 'feral' kids associate that increase in pitch and volume with being hit. Because it's the sound of somebody losing control - and it scares them, causes a rush of adrenaline and they will respond with the fight or flight response. Literally.
Just get to the point. Short sentences. Smile. Use please and thank you genuinely, not sarcastically. Use non verbal communication. Hand out praise. If they do something good (and god knows, sometimes you've got to look bloody hard for it - it might be in the playground or a week later where you see them helping another staff member or a Year 7 who was crying), give them achievement points for it, send a postcard home, call Mum and, instead of her usual 'Oh God, now what?' or ignoring your call, tell her/leave a voicemail to say that you wanted her to know that Ashleigh did x or y really well/was very kind/worked very hard in your lesson today.
In all my time, I've met one kid who had absolutely zero redeeming features. And I'm sure that somebody somewhere was able to find one good thing about him.
For the person who said they saw future inmates in their school, what they mustn't forget is that they were also looking at past, present and future victims at exactly that moment. Only seeing the first means there is no chance of addressing or preventing the second. And that starts with you being under control and talking to them, instead of at them.