“TIMSS and PIRLS testing shows that are [our?] public school kids compare rather poorly to students from a great number of other nations.
Perhaps you’re aware that the sampling methodology and analytical procedures of those studies have been called into question?”
There is always someone or some entity willing to cast aspersions on any study...or, in this case, testing...that demonstrates the failure of government schools.
There is generally someone or some entity willing to cast aspersions on any study, on any highly charged issue, if they don't agree with the results. That doesn't mean they aren't correct.
Methodology and analytical procedures are important, whether or not you agree with the findings. There are a lot of poorly done studies out there.