I was taught this in High School and I know that it is still taught. We learned it because the option for such (and many other) errors was a zero on the work and likely an F in the class overall.

Teachers have a lot less latitude nowadays; see [1] for an example that is shocking in the 1960s context.

1. https://www.cbc.ca/news/canada/edmonton/teacher-who-gave-zer...

This was definitely still taught in my public high school in the 2010s - if they stopped teaching this, it was very recently.

Granted, the teacher that tried to teach me this had no understanding of it themselves and would incorrectly mark answers wrong when they had the correct number of significant digits, so it was pretty botched in my case. Still was attempted in the curriculum though.

I think some of the problem is that you can get into computing through many pathways now, and you don’t have to come through some science and math stream from high school. Even when I was doing physics I always had to remind myself of the accuracy.

Significant figures have always been taught in chemistry courses. I remember students getting confused at notation like "100. g" representing 100 grams with 3 significant figures.

I don't remember it in junior high, which for me was the late 1970s. High school yes, definitely.