Wow. A lot of K-12 students probably don't even know their own SSN off the top of their head, much less understand the impact of having it stored in this way. I can't fathom why it would be necessary for the SSN to be tracked by the school. At most, the school district as a whole might want a record so they could make sure kids are getting schooled but putting that into Canvas doesn't make any sense to me.

That is a big yikes, but definitely not the norm. Most school districts switched from using SSN as their SIS identifier decades ago.

They already have your SSN, as does anyone else who wants it.