Strategy to ensure educated workers in Tropico 3?

Solution 1:

Build a high school as soon as it's needed, but not sooner.

It usually makes economical sense to hire up to four educated workers to start your industry, but after that, you must get the high school and the university.

And make sure the educated jobs are payed well, that is, 40% over the average uneducated workers. Else people won't bother about studying.