Schools Pupils' Reports or without apostrophe?

Solution 1:

There is no grammar rule against consecutive possessives; saying something like Mary's dog's bed's pillow's color matches my shirt is grammatically acceptable. It is, however, a stylistic issue as it doesn't read very well (My shirt matches the color of the pillow on the bed Mary's dog sleeps on is still a bit unwieldy but definitely better).

In other words, school's would imply that there's only one school whereas schools is just wrong. If there are multiple schools, you should write schools'. Regular punctuation rules.

That said, I wouldn't use either as a title. It's confusing at best. If the report in question is by the pupils, then it should just be (School) Pupils' Reports to Parents.