We recently moved and the school that he goes to does Guided Reading to determine what level they are reading.  His teacher said that she placed him at level H because he doesn’t do well with reading comprehension or otherwise he would have been a higher level.  Is there a list that I can find out what level books are and also is there anything that I can do to help with reading comprehension or is that just a n age development thing?

I'd suggest that when you read with your (son?) that you ask him questions. Who are the characters, the setting, what is happening at the beginning, middle, end. You could also stop him as he is reading and ask questions along the way.