Well, you need one if the instructor makes it a requirement, which my kid's high school does. They're actually tested on linear regression, but they don't know how to compute sum of least squares: they know how to type a list into their calculator and run the least squares function. It's on the exam, and if they don't have the TI graphing calculator with that exact function programmed into it, they fail the test.
I'd LOVE for your kid's 0 test score to go viral on social media and get kilobucks of revenue from the 15 minutes of fame to pay for college.