It could just be that better read classical liberals tend to favour freedom in education (and perhaps freedom in other areas) and it’s not Friedman specific. Is it worth testing whether the effect from Friedman is greater than having read other liberal thinkers?
I’m sorry to report it, as I like and admire Friedman rather than just admire Hayek, but a test comparing Friedman readers and Hayek readers (Hayek being the second most popular classical liberal writer among classical liberals, after Friedman) suggests that Robert is right. Hayek readers are slightly more likely to give the ‘correct’ classical liberal responses to questions on school curriculum setting and funding.
They are heavily overlapping groups: 80% of those who have read Friedman have also read Hayek, and 91% of those who have read Hayek have also read Friedman. Disentangling influences (if any) would be difficult. But as Hayek is heavier going than Friedman, perhaps this suggests that it is the more dedicated classical liberals who have taken the Hayek challenge, and these people are more likely to think that competitive curricula and private education delivery are the right policies.