School is a lot more lax about it because it's so much more difficult for them to kick you out.

When I was at school we would sometimes turn up over an hour late or just skip the day altogether. Was a culture shock when I started my first job and got a roasting for being 5 mins late.

Ask any teacher, and he/she'll have plenty of stories about parents who do nothing to teach their kids these habits, or even exactly the opposite of that.