How can i be math teacher when i grow up?

Well... you would have to start studying really hard in 7th grade and make sure you keep getting straight As. Behavior is important too. Then... you would have to get into a college where you can major in math... so yeah. Good luck if you plan on doing this! 

If you want to be a math teacher, first of all, you should be able to do math problems with no trouble at all, the problems will depend on what level you are going to teach.You must also be able to explain each and every step with patience because being a teacher can be stressful due to the lack of intelligence of some students.