While I agree with all of the above, allowing your villagers to exercise and using the portion that makes the villagers excercise also helps build up the skills. I faced this same problem when I didn't have builders to start on the Stature. It was suggested to make the portion several times and have everyone partake. After I made the portion the fourth time, my adept builder began a Master Builder ans moved trainees to adept, then Masters. Now, it is the every other portion I make to assure each villager has building skills.
I hope this helps.
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