> How does a parent (especially one that is illiterate) compare between educational opportunities for their kids?

If you have a significant number of illiterate parents they could hardly do worse than your current system!

They can judge by reputation, talking to parents with kids currently in a school, etc. IMO that is better than publishing metrics because then schools focus on the metrics: this is a huge problem in the UK where metrics are published.

In my experience parents (regardless of educational level) make better decisions than the system does, and there is research to back it up (outcomes for home educated kids for whom parents make all the decisions).

As opposed to the current market for education?

Parents know which schools are good and which aren't. They are intrinsically interested in their child's education in a way that no one else is. It's an obvious solution.