Comment by float4

> he made his students work use pens while taking his tests

This is very common in the Netherlands, I think that's why it was a rule of his.

In general, the Dutch education system seems to be against pencils (at least this was the case until recent; I'm Dutch and mid 20s). You're tought to write using a fountain pen, not a pencil. In high school, you're allowed to switch to ball point but absolutely not to pencil. In university, write with pretty much anything you want, but... not with a pencil. If you do take your test with a pencil, there's genuinely a chance your teacher will give you a 0, although most of the time they'll probably be forgiving.

I majored in CS in the Netherlands and every test was done with good old pen and paper. Students still make mistakes all the time, which is why everyone uses a scrap sheet.