Very poor judgement indeed from the teacher.
As it turned out, one student definitely had personal experience of losing someone to suicide, so that's just utterly insensitive - but any of the others could have had the same experience too, and just not spoken up about it.
I can't believe anyone would think this was a good topic - it's beyond "challenging", beyond "imaginative" and into insensitive and really disturbing. There are still entirely too many teen suicides going on, it's just not appropriate!
I don't feel sorry for the teacher, really - the school has taken responsibility and apologised, the teacher will be (hopefully) reprimanded and strongly advised never to do such a thing again.
There's a big difference in discussing suicide objectively, and personalising it by making the children write about it themselves, ffs!