I make a good chunk of my income by writing textbooks-and-other-educational-materials.
While TX has a great deal of influence in the textbook market, it’s increasingly common for publishers to put out multiple editions of books, each designed for a different state. How many states depends on budgets and so on. Typically, though, you’ll have a “national” edition that is meant for the so-called “open territory” states, where there is no centralized state agency that approves textbooks and textbook choices are made on a district-by-district basis (Ohio, New York, and Pennsylvania are examples of open adoption states, which are most common in the Midwest and East). Then there’ll be a “Texas” edition, which reflects Texas educational standards (and Texas values), and often other editions for other “adoption” states as well (the states with centralized boards: TX, CA, FL, and others, mostly in the South and West).
How different the textbooks are depends again on budgets. I recently worked on a text designed for the state of Georgia, which was a 50% revision–that is, we could make meaningful changes to half the pages in the National book. Arkansas was getting a version of its own, which was about a 25% revision IIRC (I didn’t work on it). Florida gets more than 50%, I believe, and TX and CA get pretty much whatever they want.
Part of the thing is that standards can be very different from state to state. As a silly example, 1st graders in Texas are expected to be able to use the numbers 1-99. 1st graders in most states are expected to use 1-100. So you’re putting together a page in which you want kids to practice adding 10 to a number that’s a multiple of 10 (50+10=60…). Texas isn’t going to like it if you ask them to add 10 to 90. OTOH, other states will wonder why you aren’t asking the kids to go beyond 99. Will Texas reject the whole program because of one problem that asks kids to do something beyond the scope of the standards?..Probably not. But publishers are understandably edgy about such things.
Fractions are another example. In first grade, TX wants all fractions to be in word form only (that is, one third instead of 1/3). Some other states expect kids to write and read fractions at this stage using numbers. And I’m pretty sure that a couple of states (Michigan? Don’t quote me) leave all formal work with fractions to second grade. That doesn’t mean a teacher won’t cover fractions if they’re in the textbook, just that it won’t be “on the test” and a textbook committee might not be inclined to buy the book if it’s got a lot of that stuff in it.
One more thing: textbook adoption states like it if you emphasize their geography, history, etc., even when it’s tangential. To use math as an example again, grades 3 through 6 texts often use problems based on real-life scenarios. Here’s a population sign at the edge of a city: write the population in word form/expanded form/whatever. Here’s some driveby information about a (real) wildlife refuge somewhere; let’s suppose that there were 674 brown ducks and 358 green ducks… In a basic national textbook these images and stories will be drawn from all over the country. Texas, though, would very much like to see the population of San Antonio on that highway sign, not the population of Salt Lake City, and they want that wildlife refuge to be somewhere in east Texas, not somewhere in south Jersey. Small things, but they add up. The rule of thumb in the industry these days is that adoption states will prefer a state-specific book of middling quality to a non-state-specific book of better quality.
All of which is a longwinded way of saying that states REALLY like it when the text is written with them in mind, and that Texas is big enough and important enough that textbook publishers want to give them what they ask for, and that in the long run this (somewhat) lessens Texas’s influence on books that are marketed to other states. Which, in my not-so-humble opinion, is a good thing.