Secondary Teachers - do you mark other classes' books during a lesson?

[CeliaFate]

Dd came home and said she'd been in the IT suite for maths, playing maths games as the teacher was marking books for another year.
Surely this isn't on? Before I complain I want to ask secondary teachers' advice about this practice.
I can understand marking that classes' work 1:1 so the teacher would need the others to work independently, but not to basically keep themselves occupied while she marks books.
Am I missing something, or would you complain?

Nope - unless my class were doing individual timed assessments where no (or minimal input) was required from me. I'd speak to the teacher rather than go directly to management tbh.

There are other issues, such as using her phone in class, using the computer to book concert tickets which I've written a letter to Head of Year but haven't posted yet as dd doesn't want the teacher to know it's dd who's complained about her.
I can't speak to the teacher (we're a 30min car journey from school so dd goes by bus) and if I was to write to her, she may take it out on dd.
Not sure what to do now, but definitely not happy.

That is a whipping offence in my school

I'd only do that if a class were sitting a test or assessment.

And using his/her phone and booking concert tickets??!

Pupils would actually challenge me if I did that - never mind parents!

Yes I agree, would only do this (or get the chance to, frankly) if a group was doing a controlled assessment of some kind which meant they were sitting in silence for 30 mins or so.

Thanks, it's not me being out of touch then. I'll send the letter to the HoY.