The Bible is clear: We are not here by accident; we are here because God put us here. God told Jeremiah, "Before I formed you in the womb I knew you, before you were born I set you apart; I appointed you as a prophet to the nations" (Jeremiah 1:5).
Think of it: God knew all about you even before you were born, and He gave you life and put you on this earth. The same is true of every human being; every person on this earth (even those not yet born) is important in the eyes of God. Don't ever scorn or ignore someone because they are different from you; God calls them valuable -- so valuable that His Son gave His life for them.
But notice something else about God's words to Jeremiah -- God put him here for a purpose: "I set you apart; I appointed you." The same is true of you. In the years ahead you will face many important decisions -- but don't make them on your own. Pray about them, and seek God's will above all else. God loves you, and His will is always best.
Treat your teacher respectfully and ask God to help you be the best student you can possibly be. Don't argue with him; little is usually gained from that. But let the teacher know of your faith in Christ, and pray that you will be a witness to everyone of Christ's peace and truth.