It is true that I do not always agree with how states, school districts, politicians, etc. use the results of standardized tests. The results are too often used as a way to justify funding and teacher's jobs when most of us realize that standardized tests show you a piece of the picture and not the whole picture.
However ...
As far as the student is concerned, standardized tests are kind of annoying and kind of a pain in the butt, but that's about it. They don't count for a grade. There's no penalty for failing (or not doing well). There isn't even a reward for excelling. It's just walk in, take the test, congrats you're done.
There is a tremendous long-term benefit for students taking these standardized tests. It really should give them lots of practice at taking these kinds of tests so that when they have to take the ACT or SAT or a placement test or any other standardized test they will be much more likely to be relaxed and not too concerned and just do their best. It's so unfortunate when students arrive for the ACT and are just an absolute mess and convinced that it's a "do or die" situation.
The whole point of the standardized tests was originally and really should be today a way for teachers to get an good idea of how well their students are learning so that they can make adjustments in the curriculum and in their teaching in order for the students to learn better. The reason these tests were originally called "Student Assessment" is because they were designed simply to assess the students and see how they are doing. No blame intended. Just a way to measure. Just as in any other area of society, it is beneficial to stop, take a look at things and assess how everyone is doing and how things are going to see if there are ways to improve.
Whether you agree with standardized testing or not, I think it really is in the best interest of any student to just let them take the test with the rest of their class.