what documents do i need if I want to work in China as an English teacher for a year?

You need to apply for a work visa (Z) to China. For Z visa application, you need following documents:
1. Permit for Foreign Experts Working in China (original) issued by the State Bureau of Foreign Experts (original);
2. A visa notification form (should be used within 6 months since its issuing date) issued by an authorized unit in China (original). Note: your school is able to get these two documents, you can contact them first and send to them your resume and other papers required.
3. Original passport which has more than 6 months left before it expires from the date of application and sufficient blank visa pages (18 months and more left if intended stay in China is more than one year).
4. One completed Visa Application Form with a recently-taken passport photo.
General processing time needed by the Chinese embassy is 4 working days.