一般before前后的时态不同.
有的情况是前后都是过去时.he went to school before his mother went back.
这种情况在特殊条件下可以都改为现在时表示平时的、极其一般的、规律性的情况.
he always goes to school before his mother goes back.
有的是前面将来时,后面现在时.he will go to school before his mother goes back.
before本身是个区分时间先后的词.要想前后时态都一致的情况极少.