[wongarsu]

In Germany this was part of the physics curriculum.

It made sense since order-of-magnitude estimations constantly come up naturally in all fields of physics, whether you are asking "is this plausibly possible", "what kind of instrument do I need for this measurement" (and later "can we even measure this in this setup") or "are the results of my experiment plausible". There's a reason we joke that to the physicist g=10 and pi=3.

It's difficult to test this kind of thinking in a written test without turning it into something entirely different, but not everything in school has to be on a test. Typically half of our marks were made up from classroom participation.

[pklausler]

Once you learn how to use a slide rule to estimate a calculation to just one or two significant digits, you no longer need the slide rule.