Charter schools are generally considered public schools, but generally aren't called "public schools" due to the charter structure. "Public schools" in this example are TPA (traditional public schools). TPAs have higher per student funding than charter schools.

You are presenting a generic correlation between downward trending test scores and prevalence of charter schools. Are there any studies with a real correlation that corrects for other factors? Let's remember that correlation is not causation. Especially consider that achievement was already on a downward trend and that 10x number you quote is only resulting in 6-10% of all public school students today. Even if there is a correlation with the number of charter school students and a decrease in test scores, what is the actual reason or mechanism? Just saying overall scores are still going down and charter enrollments are up doesn't show anything.