I no longer have the textbooks obviously, but it was just a regular gymnasium in a provincial town (Leeuwarden), we were using the standard government recommended VWO textbooks too, just under 20 years ago. I'm pretty sure it was in the textbook because the teacher was not the type to go off book and teach us something not needed for the tests.
We had those electronics circuit practice boards and you could hook multiple up together to make a half adder.
A group of students that were acing the tests and finishing their homework were spending a couple weeks of time in the back of the class assembling a full adder out of literally all of the practice boards the school owned. I wasn't acing any tests and wasn't finishing my homework on time but I joined them anyway because it was more fun. My contribution was realizing that we could use the relais as and and gates, doubling our resources enabling the completion of the full adder.
