(Writing this from DC POV.)
I am in year 13 at school. My school’s late policy is that you can be late once a week without any penalty. If you get two lates you get put on a report and have to turn up early for 2 weeks.
I don’t see the point of getting in on time just to sit around in form time or to go to an assembly. So I choose to make the most of the system that is in place and deliberately go in late once a week.
In case it is relevant, I have the second highest voluntary service hours in the school (this is for things like helping younger students, doing clubs etc) and I am predicted the highest grades. I’ve never had any detentions for behaviour etc.
My form tutor mentioned my punctuality in a recent parents meeting and my parents think I should just be on time. My view is that I am just making the most of the system the school has set up.
YABU: get yourself to school on time
YANBU: fair enough, be late if you want