I'm in year 11 too. First I would tell you to relax, don't stress too much about it cuz stress just makes things harder for yourself.
Your friends have their own lives. Everyone is different, some are born with unique talents so they can easily get stuff into their heads and do not need as much concentration. Because of that u must know who you are and what you are aiming for.
The next stage is to not make fun of something the teacher is trying to put into understanding. In my experience, people laugh at teachers due to peer pressure of mock what they are studying not knowing that they are mocking themselves.
Push yourself harder by thinking about your future, do you want to be successful?
When you are about to procrastinate your homework tell yourself that you don't want to be a homeless person; you want to grow strong and provide for your family. Lastly think about your house to be your parents house and that you need to build your own and by doing that you have achieve well. I hope this was helpful ☺