@134318c2 My school math teacher -- and RAF navigator --  told me that Britain lost most of its mathematicians in the air over Germany, and basically it wasn't until the 1970s that there was enough expertise in *teachers* for high school students to learn math as they did before the war. 

 @0bf09504 

The generational and living nature of knowledge is something I think people underestimate. 

It takes time to develop good enough teachers... to teach good teachers.