There is Key:isced:level for the property you want to express, which is an international standard.
Added: https://wiki.openstreetmap.org/wiki/Proposed_features/grades. Thanks :)!
You removed the warning label from the Ambox. However, can you provide any evidence that even in Canada the grades below zero and above 13 are in use in real life? Otherwise we might move your whole page to your user space for further development. Please note that the proposal you refer to is only a draft that you created yourself simultaneously, and nobody has agreed with that. As said in other context, you cannot retro-define a different value system just by writing a wiki page.--Polarbear w (talk) 07:58, 11 August 2017 (UTC)
It should be useful for all schools on OSM, including kindergartens, whether toddler education, infant education, etc., is provided, and in universities, for determining whether undergraduate or postgraduate (or both) education is provided. I made it so that it covers all types of education. In Canada, usually schools offer toddler education to Grade 5 or even to Grade 12, so it's very useful to have one encompassing system of tagging. Also, in Sweden, Grades 14 (ages 19-20), and 15 (ages 20-21), called "Fourth Level" and "Fifth Level", are featured in gymasiet (ongoing school). I've also edited the ambox again so that the tagging system is not redefined, just added to :). Thanks :), EzekielT (talk), 09:24, 11 August 2017 (UTC).
- Thus I conclude that even in Canada, numbers below zero or above 13 are not in official use. They are just applied by yourself. Do not expect everybody to follow your undiscussed idea. As you just discovered in your Sweden example, different terminology is used in different countries. That's why the ISCED levels are useful, as they are already normalized internationally. Which grade are you in?--Polarbear w (talk) 15:01, 11 August 2017 (UTC)