The twelve years of schooling will be divided into three four-year cycles

Ivan Yefremov : paleontologist, geologist, science fiction author and social thinker
“The psyche is wearied and becomes sluggish where there is a uniformity of impressions and perception becomes duller. The efficiency of teaching and upbringing grows less year by year. That is why the twelve years of schooling are divided into three four-year cycles and you move to another school after every cycle, each time to a different part of the planet. It is only the babies in the zero cycle, from one to four years, that do not need any change of place and conditions of upbringing."
"And why does each cycle have separate schools and separate living quarters?"
''As you little people grow up and are trained you become qualitatively different beings. If different age groups live together it makes their training more difficult and is annoying to the youngsters themselves. We have reduced the differences to a minimum by dividing the children into three age groups...”

Novel "Andromeda"