"What is 6+1*0-2/2?" memes/threads on Facebook have taught me that infix math notation is more or less completely unfamiliar to the general population. At least sexprs are fully parenthesized.
If you are talking about order of operations, all of the sixth graders that I teach know how to evaluate that expression. While it's true that I had to teach them * means multiply and / means divide, they can quickly pick that up. Our school is all honors and the students are above average intelligence, but they are not all math or tech geeks.
On the other hand, I have taught courses at the high school level at the same school based on "How to Design Programs" [1] using the Racket language. Although I can explain the concept of (+ 6 (* 1 0) (/ -2 2)) rather easily, the students make mistakes writing expressions for several weeks.
I wasn't entirely serious, and I believe sixth-graders can evaluate infix expressions with correct order of operations, but it was adults I was referring to, many of whom have long forgotten.
