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I could not find any text in the standards suggesting the need for students to convert … from customary … units to SI units
5.MD.1 is explicitly restricted to conversions within a given system. But 6.RP.3d is not restricted in this way:
“6.RP.3d. Use ratio reasoning to convert measurement units; ….”
I would interpret this language to include converting cm to in, or vice-versa.
(By the way, I don’t think the larger question in boldface belongs on a discussion thread about 5.MD.1. You might consider finding another thread in which to post that question. I will say that both assessment consortia have websites with a great deal of documentation about how they are interpreting specific standards and the Standards as a whole.)
I’ll try to offer some thoughts here and I hope they’re helpful – although I’m not sure what is meant by “the metric system.” The system of units that is used for scientific purposes is the SI system.
Time is one of the base quantities in the SI system. The SI unit of time is the second. Minutes, hours, and days are outside of SI, but these units are accepted for use within SI. (Information about the SI system is found here.)
If you look in the previous grade, you’ll see that standard 4.MD.1 is explicit about hours, minutes, and seconds. So it would certainly be natural for hours, minutes, and seconds to be part of the continuing thread in grade 5.
(It is often helpful to look at progressions across grades in order to shed light on a specific standard within a single grade.)
I’ll offer some additional comments in case helpful or at least interesting…
When a standard “includes” a lot of things, there is always a risk that it will translate into a laundry list of to-do’s for students. The granular approach to standards exacerbates this risk. (See Grant Wiggins on Granularity)
In cases where a standard “includes” a lot of things, maybe instead we can think of it as an opportunity to find unity in diversity – to write the kinds of problems and lessons that put ourselves in a position to say to the students, “See? It’s all the same!”
So, including time in this standard could be a virtue if it helps to give the subject of measurement a unified character. (I’ll note here that time plays a role in my post “Units, a Unifying Idea in Measurement, Fractions, and Base Ten”.)
A final note in favor of coherence…cluster 5.NBT.A is designated ‘Supporting’ by the two assessment consortia (see here), and that is a reminder that instead of treating this work as yet another disconnected set of tasks, unit conversions might be positioned in such a way as to support of the major work of grade 5. The parenthetical example in 5.MD.1 involves converting 5 cm to 0.05 m; this begins to gesture at how the work of 5.MD.1 relates to other grade 5 work (cf. 5.NBT.A, 5.NBT.7, and 5.NF.B). So in addition to teaching students the enumerated concepts and skills of measurement, the body of work relating to 5.MD.1 could also give students practice with, and insight into, place value, decimal computation, and fraction operations.
