True story- I was once preparing for the Praxis test in NJ so that I could pursue a math teaching career. The Praxis math test is basically Calculus 1st and 2nd semester, but with one real twist.
It's all multiple-choice, but the answers tend to skew towards rational numbers with three or four trailing digits (aka 37.1253) instead of simple integer answers. So you can't pass the test by just knowing calculus theory- you've got to be able to use your calculator.
There are 50 questions, with a 2-hour time limit. You've got just over 2 minutes a question. So you've got to know how to use the calculator fast.
When I took the test, I was out of college for a decade, and had never used a TI calculator before (and that's all you were allowed to use). I took the time to use the calculator, reviewing the entire manual and working through a set of problems so that I'd be able to use the calculator quickly during the exam.
When I got to the exam, there were multiple test-takers taking the calculator out of the packaging for the first time.
I finished the exam quickly (and finished with a score in the top 1%). As I left the classroom, it was obvious some of the participants were not going to pass the test because of their struggles with the calculator. They may have had immense potential as math teachers, but since they didn't know that brand of calculator, they were doomed to either retake the test (and it wasn't cheap) or pursue another line of work.
And THAT'S how deep TI has its hooks into the math education business.
(PS- I didn't become a math teacher- I took up IT consulting instead, but it had nothing to do with the calculator.)