I have been teaching a long time, and I know from experience that 50% of students will tell me that 3^2 = +9 on a test or a final, despite having discussed it a few times in a course.
When I first started teaching I taught calculus and precalc. Piece of cake. Then I started with an Algebra I class and couldn¹t connect at all for the first week or so. I was ready to believe I couldn¹t teach. I simply could not explain how I got the right answers when evaluating expressions... Then I discovered the order of operations (PEMDAS to some). A definition of the order of operations which I had so internalized that I didn¹t know there was a rule for it. Since that discovery I¹ve been a wonderful teacher. :-)
So... I must be missing something that so many of my students think 3^2 is +9. What is the rule I have never discovered?
Full disclosure: I think k^2, k a constant, should be banned from mathematics texts and tests. -x^2, x a variable, evaluated for say 3, absolutely (no pun intended) but not 3^2.