Is dimensional analysis part of Math 6?

[jmasia]

I was looking into the ratio and proportions progression in math 6. I know that 6rp3 talks about unit convention as part of the standard. I also know that dimensional analysis uses ratio equivalences to perform conversions. Is it an appropriate tool at that grade level and if so can you advise on how to approach it. Thanks.

[Bill McCallum]

I think Grade 6 is early for dimensional analysis. That comes in in the high school standard:

N-Q.1. Use units as a way to understand problems and to guide the solution of multi-step problems; choose and interpret units consistently in formulas; choose and interpret the scale and the origin in graphs and data displays.

[jkerr]

I posted a few days ago about discrepancies between language in progressions and language seen from PARCC assessments. Well, here is something similar.

The RP progression doc states that in high school and beyond, students will write rates using derived units, something like a/b units/units (using fractions). Essentially, they will move away from the wordier version of a/b units for every 1 unit and write them in a more concise manner. This makes sense in conjunction with your statement about dimensional analysis. So, how is the following Grade 6 Smarter Balanced question fair?
Item #25 on page 27)

I would expect students to be using ratio tables, double number lines, or other ratio reasoning to convert units, not working with derived units. This seems like an inappropriate assessment question.
Am I missing something here?

[Cathy Kessel]

On the better-late-than-never principle . . .

The SBAC question does not have units written in the form units/units. If it did, dollars per pound (the derived unit) would be written using a fraction bar, e.g., dollars/pound or USD/lb. Instead, terminology is as in 6.RP.2.

[jkerr]

That’s because they fixed the item. I’m going to act like it’s because of my post 🙂
I’m glad things are being cleaned up.

[Cathy Kessel]

Thanks for the clarification. It’s encouraging that SBAC made the change.

[Author]

Posts