Young kids are often morning people, but teenagers biologically have something going on that makes them almost universally not morning people. Forcing teenagers to go to school in the dark for several months of the year can make it very difficult for them to get to school, and leave them half asleep during school. This will have an impact on their grades, which can have a follow-on impact on their whole life.
We should probably start high school later in the morning even if we stay on standard time ; it's way more important if we switch to permanent daylight time.
> What makes no sense to me, is that secondary school starts earlier than primary school?
It starts earlier so it can end earlier so that there is time for sports and other extra-curricular activities?
Teachers spend time with students doing these activities, and the teachers have lives too. If high school ends at (e.g.) 2:30 pm, there's 60-90 minutes that stuff can happen and teachers still have 'regular work hours' of 8-4 (a shifted 9-5) so they can do things in their lives.
Doing the activities before school makes a lot more sense. It adds another selection filter, the exercise wakes up the students and calms them, and it gets rid of the excuse for starting school so early.
Activities also can stop during the really dark weeks around the solstice in a way school can't.
We should probably start high school later in the morning even if we stay on standard time ; it's way more important if we switch to permanent daylight time.