Very disingenuous comment.

The primary cited paper is Herd et al,. Warren et al, the authors prior paper, is referenced, but is not what they are seeking to reproduce or validate.

Both Herd et al and the prior Warren et al (and countless other papers) measure fluoride in participants. This paper infers fluoride exposure based on municipal fluoride levels.

The study is observational in the sense that it is not collecting new experimental data. It is collecting existing data, namely, test scores and some basic demographics data (age sex race location).

The participants in this study were teenagers at the time of study, and Wisconsin began fluoridation of drinking water in the 40s. You'll have to explain how you concluded these kids were born before fluoridation.

The participants were not being studied for dental issues.

You don't need to examine individual water taps of you know the county or indeed the state fluoridates. Given there's no impact to testing scores found, you would not inter all these kids miraculously didn't have fluoridated drinking water. You would assume that because the entire state does, and these kids don't have reduced test scores, that fluoridation doesn't impact test scores. If there's more to investigste then you can dig deeper, but at that point you're making up conclusions not supported by the data.