Much of what we teach teenagers about human biology is very recently-acquired knowledge, historically speaking. Modern knowledge about the circulatory system, aerobic and anaerobic respiration, vitamin deficiencies, etc. is very far away from the 13th Century, but has practical implications that can still be implemented, like "train your troops at altitude and give your sailors citrus fruit".

A lot of contemporary ideas about workflows and division of labour are fairly recent developments as well, (there were no assembly lines in the 13th Century), but have been internalised by citizens of the 21st Century.