In my time( many moons ago though it aint much different now) students at age10/11 would sit an exam to determine whether their years from 12 to 16 would be at secondary(ordinary) school or High (grammar,technical high etc) Students passing this exam would go to an establishment of a higher grade studying at a higher grade, better facilities, better teachers, uniforms etc. At age 16 they would be examined in up to 8 subjects in any permutation from say Maths, english,chemistry, physics, engineering science, geography, history and several languages.
A student could obtain passes numbering from 0 to 8 and these were known as "O" (ordinary) level passes.
Someone with 8 O levels would be encouraged to stay at school for another 2years to study about 4 subjects at a more advanced level to gain entry to uni.
Again at 18 they were examined on these subjects known as "A" (advanced) levels
A smart student sporting 8 "o" levels and 4 "A" levels could apply to a uni or unis for entry.
Marking was strict and more or less standard countrywide.
Kids leaving school at 16 with a few "O" levels would look for apprenticeships, and kids who never made the cut and went to secondary school would leave at 15 and get what they could.
There was always opportunity of TAFE type learning available for "late developers" and in those days education was free.
Nowadays I think all schools (apart from private) are known as "Comprehensives" but the "wheat" still has to be sorted from the "chaff" somewhere along the line.
