In the science class, dealing with the pest kids was mostly achieved just by separating them. I made the whole class stay in at one point, and the leader of all disruption didn't seem to understand the punishment :/
In the English class, the main issues could be dealt with just by saying kids' names harshly, and telling them that if I saw their phones again I'd keep them. There was one girl who wasn't really disruptive towards other students, but considered class a good time to sleep and had this delusion that she could walk out of class unnoticed. I don't know what it is that eventually worked with her, because in my last week she walked out of class and one of the students immediately pointed it out. I said: "I know, but I'm not going to bother going after her -- I know a lost cause when I see one." Highly motivating and encouraging :/ Then, in the next lesson, for no apparent reason she was constantly on-task and really well-behaved. I don't think anything I did was the cause of her sudden good behaviour.