Also, it would be interesting to take in account how many years does primary school last. Usually there is 1-2 years of difference between countries. Sometimes begin a year before and sometimes a year later, and the same happens to finish it.

So, i realize that it's not a so significant metric.

But, man, take a look to the unesco database where i take the data from... there are countries (like Canada!!) without data about primary school teacheres 😮 so... starting from there, you can't expect to get very accurate images about these "international comparatives".