CSE students at the time were not allowed calculators and as a result were better at mental maths but did not understand the more complicated stuff.
When I did my O Levels (back in 1981) we weren't allowed calculators partly due to the cost being prohibitive for some people, but mostly due to "mathematical snobbery" (Slide Rules and Log Tables were good enough for me and my father and grandfathers...!)
It does mean I can still do mental arithmetic without needing to reach for the electronics which can be very handy at times.
I'm not sure about "not understanding the more complicated stuff", personally I gave up maths at A Level (which I was told I should do because I wanted to do computing at University) because I just couldn't see the point of it!
By that point I'd already learned programing on the 8k Pet and learned a little about machine code on the
Acorn Microcomputer and in Sixth Form played around with the
UK 101 before they got BBC Model Bs which were much better.
I learned 6502 Assembly Language on the Beeb mostly through originally hacking games for infinite or 255 lives! I can still remember using a program called Exmon (Extended Machine Code Monitor) to search the code for &E9 01 (the hexadecimal code for subtract 1) which would stop the number of lives counting down or &A9 03 (Load Accumulator with 3) and changing that to &A9 FF (255 lives) which meant you could play one game a lot longer