The advantage of working with trainee teachers (Teach First teachers) when you have been teaching for a long time is that it takes you back to the beginnings of things like classroom management 1.01 and behaviour management basics.
Building Relationships and Expectations are crucial in the first few weeks. Tamaki College has a set of values called RISE (Respect, Integrity, Success, Responsibility) which are embedded into the vision and ways of working in the school. The students are familiar with these and they work well. The teacher will also set other expectations to do with behaviour, work, tools, listening and following instructions. These will all enable the development of positive relationships between teacher and students and so make the teaching and learning more productive. See building relationships with Pasifika students here and with Māori students here.
Setting up a routine and sticking to it is also crucial to developing a good and safe physical and emotional environment for the students. See the Effective Pedagogies from the NZ Curriculum and, in particular, "Creating a Supportive Learning Environment" (p.34) here, culturally responsive indicators here, and PTC2 here .
I have been working with teachers on using strategies like: use a seating plan. The students hate it but they get over it. It is a way of asserting authority in the classroom and enabling all students to learn without being distracted. We found that the best way to do this in the school's digital environment was to put the plan on the whiteboard screen so that they see it as they come into the room ie it is a non-negotiable object and with the teacher using the "broken record" technique, they begin to see that it is being done for their learning. The plan can go up on the screen each lesson, for a short time, until it becomes routine.
Another strategy is use of voice. Personally, I think all teachers should take voice lessons (I did) because, used well, it can be a very powerful tool in the classroom when projected effectively. The students also need to learn about controlling their voices as the teacher models the continuum from soft to loud.
Teaching is a complex job with a lot to learn for newbies. They need lots of support & encouragement.