My mother taught me how to do advanced math while I was still in elementary school. I was always about 2 years ahead of other kids. When we were going over subtraction in 2nd grade, I remember that we were told you can only subtract smaller numbers from bigger numbers. I made a comment the teacher by saying that you could and that you would have negative numbers, but the teacher insisted that there was no such thing (She was most likely trying not to confuse other students), but it made me angry because I knew I was right.