The testing is too long and cumbersome. MCAS test administration can disrupt an entire school for two or three weeks - even if the school isn't under reconstruction. Many teachers are fearful of not covering material dictated in the Massachusetts curriculum frameworks.
Students pick up on the concerns of parents and teachers.
MCAS is a poor assessment tool, but I do not believe that a boycott will change it. It's a bit like complaining about government but not bothering to vote. Some adults are sanctioning the boycott, and it sets a worrisome precedent. Some students are traumatized by MCAS, perhaps because it's become too important to them. But MCAS is really a test for schools.