There is a business saying that says, "You get what you measure". That's not to say that what you measure is necessarily the right thing. Instead it means that any individual or organization will adapt its behavior to maximize whatever it is that is measured. Customer service representatives who were rewarded based on how short their phone calls were simply hung up on people who couldn't be helped in just a few minutes.
The results of the MCAS tests are similar to that business saying. When teacher or school evaluations are based on how well the student body performs on an individual test, the administration and teachers will try to adjust policies and teaching styles to maximize the number of right answers. This is not good for the overall education of our children. Often, teachers end up resorting to factoid-based instruction rather than exploring the deeper complexity of the subject material.
Instead, as a school committee member, I would recommend policies which have teachers continuing to teach rich subject material, consistent with the state frameworks, with no special emphasis on MCAS preparation beyond a basic review of general test taking skills. I would also recommend a more detailed review of the MCAS results by principals and curriculum directors to determine if there is a trend in a particular subject area that requires changes to the overall emphasis of that area.