Should a teacher be educated

A few facts to consider:

• Students graduate at age 16 if they live next to the school. If they have to walk (back and forth) to the school, that walking time does not count toward education progress. This is why players are reporting 20 year old students.

• Education gives the worker a ~50% productivity increase. However, education does not make a worker walk faster. This means that hunters, gatherers, foresters, laborers, vendors and tradesmen do not benefit much from education. Fishermen, miners, quarrymen, firewood cutter, blacksmith and tailor all benefit from education.

• Having students locked up in school delays the creation of couples. This could tip a city that's on the edge into stagnation. If you have fewer than 10 children, you should probably be focused more on making more children, rather than education.

• Education also reduces random accident death, so you'll want it eventually.

So, putting it all together, I'd build a school when all of these criteria are met:

• There are more than 10 children.
• There are more than 8 workers in non-walking jobs.
• There are no more pressing needs (food/firewood).
• There are at least 4 spare laborers (+1 to be a teacher) to handle the gap created by the first wave of students.

If you do not have any available laborers then the job will remain empty until there is one avilable.

If you notice, when someone holding a job dies, there are 2 messages in the log:

"So and so the teacher has died"
"What's his name has replaced so and so as a teacher."

Unfortunately you are correct that once the students leave the school they become "Uneducated" laborers and will not return to school. This is due to children and students becoming laborers at the ages of 10 and 17-18 respectively. When a child reaches the age of 10 they have to be either a student or a laborer. If there is no available school, or the school is full, the child goes straight to laborer.

To prevent something like this happening you should always have a few laborers available to mitigate deaths. If you're truly short on workers, try pulling a few people out of jobs that aren't being worked currently. Usually I keep 2 people in builder even when I don't have a build job going and I let my Blacksmiths/Tailors/Woodcutters come and go as my supplies bounce against the cap. Some of these jobs are good to remove in order to have available laborers in times of desperation.