Towards the end of Secondary School (the last two years, I believe), I skipped school more than I went, for the fact I was being bullied, and it was become really hard for me to even concentrate in lessons. All my teachers knew I was being bullied bad, but didn't do shit about it, which is why they never contacted me or my Mum or social services or... well, anyone, about that fact I was having so much time off. It was also partly because half-way through the second-to-last year, I had a massive falling out with my friendship group over something kinda major, and I ended up being almost completely alone (but my best friend spent every break and lunch she could with me) all the time, and topping that with the fact I was constantly having people shouting at me and trying to hit me/trip me over... When I actually went into school, I got really depressed and paranoid and because of it, I ended up permanently developing depression, anxiety and paranoia issues and ended up having to see a psychiatrist for it all.
Skipping school can be justified, but only in extreme circumstances if it's for a long period of time. I'm not sure if mine is quite "justified" but... yeah. There are reasons sometimes school does more damage than good.