As a middle schooler blindly copypasting assembly to make the mouse work in my Turbo Pascal programs, can confirm that this was extremely rare in the mid 90’s. Just having a computer at home was rare enough, the fact that you were into programming? There were like 5 of us seriously into it in the whole school of about 1000 pupils.
Even now there are only about 27 million professional software engineers[1] in the world. That’s 0.3% of the population. Looking at USA alone, 1.4% of the population are software engineers. We are extremely rare.
I think it was more common in the 1980s for amateur programmers (including young people as I was then) to know assembly than it was in the 1990s and later for several reasons. First of all there was the need for it -- while there were compilers you could run on 8-bits, the limited memory space meant that the compiler often ended up taking too much of the memory you needed for your program, and so when people realized that BASIC was too slow/limited for what they wanted to write, assembly language was the obvious alternative. Secondly, the assembly languages of 8-bits was generally 6502 or Z80. These are relatively simple processors and learning these architectures (as I did myself) wasn't that hard. Once x86 machines took over in the 1990s, assembly because less attractive both because compilers were more practical because of larger memory and because x86 assembly is frankly a nightmare.
Uncommon, but not extraordinary. I did it. Only one or two others at my school were familiar with asm, but I came from a very small town (the single integrated middle and high school was 800 pupils)
