Q. Can I use my kid’s 529 plan to pay the tuition of a private high school?
No. You can only use the 529 money to pay for post-high school education. That can be college or graduate school or a technical school or some other post-high-school school I haven’t thought of, but not high school.
However, the Coverdell Education Savings Account works similar to a 529 plan and can be used for high school tuition, so you might give that a look.