Back In Time To Teach

I got this idea while browsing through the available fanfics, so bare with me if it's a little bit rubbish; it hasn't exactly got a full thought-out plan. harry gets sent back in time... to teach at hogwarts ... the same year that his parents start... but ginny has only just given birth to lilly... whats he going to do? read it's better than it sounds rated t for later