This diary entry cracked me up. I'm not sure, but I think the student was deliberately playing off of the double meaning of the phrase "good for you". I made a few minor edits for readability but the words were not changed.

(Good for you)

My mother said, "good for you." Because when I watch TV my mother said, "Are you finish your homework?" and I said, "No." So my mother said again, "Turn off TV." I said, "Oh, mom." My mother said, "It's good for you."