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I do not know about all jurisdictions, but in my region of the world, the high school completion rate jumped by approximately 20 percentage points right around that time (from ~60% to ~80%). Assuming that holds true elsewhere, it stands to reason that with more people graduating high school, more people are likely to be accepted into higher levels of schooling. With more people attending higher level schools, the increase in demand (without an immediate increase in supply – it takes a long time to build new schools and even longer to recognize them as respected institutions), means price is going to rise.