Dear Kitty,
I am a retired professor--Director of two fashion design programs, and I taught at four institutions. I preferred teaching fit, rather than grading, because grading, as done in industry does not work.
Think about a patternmaking program if you have many clients. If you sew just for your family, purchase patterns that fit the armhole best (this is the most difficult area of the body to fit). Then look at some books at the library on fitting. Industry uses a grading system that changes patterns in several places in 1/8-inch increments. Two of these areas are the armhole and the shoulder--two places where people usually don't gain weight. So, when one looks at RTW the shoulders and armholes are usually way too big.
ALWAYS make a muslin before cutting into your good fabric.
Teri