It wouldn't. The Free Market would eliminate the production of Evolutionist school-teaching, because the majority Buyers (Creationist Parents) do not wish to purchase the product.
You need to familiarize yourself with the Economics of Consumer Sovereignty. Given a Free Market in Education, you're not going to end up with any freshly-minted 18-year-old Evolutionists, if the Parents of the 5-year-olds are only interested in purchasing Creationist teaching.
Catholic schools teach and accept evolution. They are free to do whatever Catholic parents want. Yet it seems that most everyone in Catholic school is happy learning evolution; which is good, because it is something of use that the Free Market desires.
Numerous private secular schools also teach evolution.
How are you not going to end up with students who know evolution, when the #1 non public school out there (Catholic schools) is teaching evolution, and many of the private schools are also teaching it?
Consumer Sovereignty indeed! Enough people want their kids educated in actual science, not biblical apologetics, that the Free Market provides a PLENTIFUL supply of schools to meet that demand.
Do you think Catholics and Catholic schools are destined to be outbred and eliminated?