I didn't say your wife worked less than 40 hours a week, I said that most teachers do.

Incidentally, for the average to be 38.5 hours/week, that means that for every teacher working 60 hours/week, there must be about 6 teachers working only 35 hours/week or so (the study I referenced only counts full time teachers, i.e. those working at least 35 hours/week).