Tips on Sight reading both staffs at the same time. :p

Ok so my piano teacher has assigned me some hymns to learn since we're going to level 3 soon. First she asked me to read soprano and alto separately then put them together. Pretty tough at first because I never played two voicings before from sheet music. Anyway I learned that then she said learn the bass and tenor and when I went back next week try to play them together. I practiced doing this hard last week and then this week she said to do it again, not because I messed up, but because she wants me to get better at reading treble and bass at the same time! I guess you're supposed to start learning to read both when you get to certain level of reading What I need are some tips and advice on how I should go about doing this. She does it all the time when I give her a piece of transcribed music for piano. It really gets your mind confused when you read two clefs at once.