Transition inquiry

Hello teachers 

I am a teacher of English from Morocco ; I have been teaching middle schoolers for the past two years

Recently I have been transferred from teaching middle school in a rural area into teaching high school in an urban area , I have so many questions but the most important one is how did you deal with students that old ,big and careless in their studies ? how did you handle the transition of transferring from the middle school to high school??

thank you