20. That's not an article. That is the publisher's own site
Open the preview pages, it is indeed the same textbook.
But you are right in that we don't have any confirmation if all or any of the 377 charter schools use that specific book, but there are not a lot of textbook publishers in this country. There are even fewer creationist textbook publishers. So it is probably a lot more than one.
I too would like more specifics, but the AP article on private school certification does not bode well for outright denying this either.
"We don't look at the quality of the curriculum," said James Garvey of Metairie, who co-chairs the board's School Innovation and Turnaround Committee.