As a teacher and tutor of math and chemistry, dimensional analysis is always the way to get from "here" to "there" when one is working with diverse unit systems or just trying to work a path from the givens or knowns to the solution.
As a student, I didn't formally learn dimensional analysis until I was in high school. Yet, little did I know, I had been using it all along. Certainly, though, when I learned to use labeling units and canceling them to my advantage, I had a Eureka moment and both my knack for, and comprehension and appreciation of, mathematics and the sciences blossomed.
For these reasons, I believe dimensional analysis should be taught when fractions are introduced... in fourth grade, perhaps. Just a thought. What do other teachers/ tutors of math and/or science think?