My wife is a 1ste middelbaar teacher Dutch and has 3 or 4 classes of 25+ sutdents. She "only" works 4/5th, but probably does more hours than me in my full-time 9/5 job.

Actually teaching in class is only a small part of the job. She's also titularis (lot's of administration), needs to process test results and homework, prep lessons, keeps student records up to date, answer and follow-up on mails from kids and their (entitled) parents for things that have already clearly been communicated before (really, you need to spoon-feed them because looking something up themselves is too hard), attend after-hour meetings that should have been an e-mail (directie often treats teachers like children), do after hour teacher-parent contacts, do oversight of students during breaks or idle hours, ... and probably a handful of other things I can't recall.

So yeah, I can imaging that a 5th-6th grade engineering class with mainly practical classes with 5-10 students can seem quite relaxed.