I am going to be a teacher.这个句子的意思是:我打算当个老师。此句运用了be going to 结构，be going to 结构属于一般将来时的范畴，如果就句中a teacher提问，则用特殊疑问代词what引导变特殊疑问句，答案是:What are you going to be？意思是:你打算当什么？

What are you going to be be

这是be going to的特殊疑问句，其结构为：

特殊疑问词+be going to 的一般疑问句？问什么用什么特殊疑问词：what who which where when why how 等

例如：What are you going to do this afternoon

Where is he going to play football this afternoon