I already wrote you a long response, but here's an example I think sums up what I'm trying to say about standardized tests:

When I'm not under the pressure of a test, and have a particular curriculum to cover one week, such as how to describe your house, for example, I start by asking simple questions like, "How many bathrooms are there?" Some kids pick it up right away, and other kids struggle. I continue to call on all the students an even amount of times, so they all get to practice speaking with me, but I ask different questions of different ones. "How many bedrooms are there?" versus "How many armchairs are there?" for example. Everyone benefits by the listening, but the quick kids get an added challenge and the slower kids get to practice and reinforce their speaking instead of just staring at me blankly until I tell them the answer and ask them to repeat.

When I am under the pressure of a test, then I have to make sure every kid can describe their house. This means that once the quick kids get it, I have to stop calling on them so that I can spend more time calling on the slow kids so that they get more practice time. I end up asking some kid how many armchairs are in his house a dozen times, asking him to repeat the answer again and again until he gets it. For these students, this can be really beneficial, but it's at a cost to everyone else in the room.

You say that maybe they need attention outside the classroom, but the problem is that I have no control over that while still being held responsible for the test scores. If a school's funding or a teacher's salary is dependant on student performance, then we don't get to say, "Well, too bad, he should've gotten a tutor." Instead, we use all our time essentially being that tutor for a small number of students.