It was true in Greece, Serbia and Bulgaria all of which retained their educational systems, run by The Church, into the 19th century. Serfdom was gone in Greece under the Empire, as was also true in Serbia and Bulgaria. The Turks brought back a sort of serfdom but not like in Russia or Poland or Rumania. I've never heard of anything like serfdom in Greece in the time since Christ but maybe at one point there was.
In Greece, Serbia and Bulgaria, during the Turkokratia, educating the people was forbidden so The Church ran what were called "hidden" or "secret" schools which the children went to at night, "by the light of the moon" to meet with the priest in a cave, or cleft in the rocks or the forest or in the church crypt where they learned to read and write and "of the things of God".
Here's a little poem every Greek Orthodox child, me included, has learned (in Greek of course) for well over 100 years:
Little moon, so bright and cool
Light me on my way to school
Where to study I am free
And God's Word is taught to me.
Here's a famous painting of one such Krifo scholio:
