Take the initiative to teach yourself or change classes. Ask your coordinator, or even the principal, if they dont help, tell your parents and they could ring the school, seems like your creating a fuss, but sometimes, unofortunately, teachers will only take your parents seriously. But, before you change, talk to people from the other classes and find out which teacher seems to be the best for you, if your school asks you what class you would prefer to go into, choose the one with the best teacher, and one where you dont have people that you wil be talking to a lot and disrupting your class work. That was my mistake in year 10, had a class where all my friends were and we spent more time making the substiture say "whaddup in the house" to the next teacher who walked in than working. (this is true, he actually did it, to the science coordinator
)
If you need help on certain things, ask us, we have plenty of people here on BOS who im sure are willing and reading to help on what you need.
If you need more help, you could always get tutor, but if you cant afford it, we can still help, post up your problems, ask questions and you will learn
There are so many people on here dedicated to helping people in your situation, just ask away.