Everyone is asking me this. I can't have an opinion because I am not an expert on the tests neither am I in the back rooms of the schools you want to attend at middle school or high school. For several years, I have contacted many principals from popular, high performing district middle schools in the Districts that I cover. They have all, with one slight exception, assured me that they are NOT using the tests as a screen for admissions. MS 51, the one exception, has a clearly stated work-around that many parents of kids with good grades are considering a strategic advantage. For all the anxiety, the middle school process is local and exceptions seemed to be pretty tolerated. There is also a pretty active opt out culture in many of these neighborhoods and the middle schools want to consider all students.
With that being said, the tests are being used generally for high school placement, sometimes in a pretty significant way and in such a big system it is often hard to make a nuanced case in a giant admissions pile. But people are. If opting out at 7th grade were just a political act, I personally might not have the balls to do it in 7th grade (possibly yes, in some elementary grades). While I am a blustering, brave person in many situations, there are so many working pieces to this high school choice process and if I thought my kids would do 'fine' - I would probably just keep my head down, toe the line and take the test. For years there have also been families from private schools and IB schools and progressive schools that have had all kinds of random grades and assessments who have gotten in the public high schools that they have tried for. What they know that the opt out families need to understand is - now it is on you to find out what each individual school will look for and need instead. It takes some leg work and forethought.
If you are opting out at 4th or 5th grade, and you have a child who might be a candidate for a citywide screened school (BSI, Anderson, NEST+M, Hunter, etc.) you need to determine what threshold they will use to allow you to apply. And that is information that may not be readily available at the moment that those tests are being given. You need to think a year ahead. I know generally what is going on, but don't come to me for assurances that opting out will not close some doors. It may not ever matter, but I know better than to make those guarantees.
Likewise, if you are considering opting out for 7th grade, you should know the deal for high school way ahead of time and you should have gone to the HS Fair in the fall of 6th grade and stood before the principals of each school that you love and ask, "if my child opts out, what criteria will you be using to rank them in your school." You will naturally want to call me to get a guarantee that you will be fine, but I am not ready to take that responsibility. You likely will be fine, but only you know all the moving pieces about your child's profile and only you can really ask these questions.
There is one other issue that has come up. This year, I have been talking to families who have been opting out every year and now that they are staring down the 7th grade tests, afraid that not taking them will screw their kids out of some choices that they want - the tests have become a giant frightening monster that must be avoided at all costs to their children. It is just common sense that taking the tests for the first time in 7th grade when they can be really high stakes is not a good plan. We unfortunately live in a testing culture; 4th grade, 7th grade, ISEE, TACHS, SHSAT, AP, SAT, ACT, GRE, MCAT, LSAT, GMAT...
After school is done, happily we don't seem to ever be tested again (thank gawd), and our life's success is not dependent upon them, but until then it is always hard to opt out.
I am not pro or anti testing. The schools and the kids need assessment tools. I hate bad tests that don't do their job and lead learning rather than following it. I want to fight against the a culture that is wrongheaded, but I am a coward, nervous about throwing my child onto the barricades. In the end, I suppose that I would be a pragmatist, fighting when I can, keeping my head down when I need to, and helping my child stay strong as a fighter for what they feel is right and staying whole and confident to also live in the world that is.