You have to understand too that teachers commonly help students grade wise, they don't necessarily push them to their full limits, and simply give them beyond easy work if they are failing. Teachers will commonly just give retakes on tests that the students previously bombed, thus raising their grade.
SAT's really challenge this, it puts kids on the direct spotlight, if they do not put forth the effort and study, then they wont pass, simple as that. There is no going back, you need to actually work hard and there is no one there with you holding your hand.
I don't necessarily agree with that. Some teachers and classes allow students to retake a test. I don't think that this is allowed for those states that have standardized end of course testing.
In my district, it is required for all teachers to allow students to take retakes atleast once, now, I am sure all districts are not this way, and that isn't necessarily my point, my point is that a majority of places issue retakes, and actually encourage it. I have had teachers even issue class retakes, last week in Science, over 70% of the kids failed the test, as a result, the teacher decided that it would be smart to give everyone time to correct their papers in class, this resulted in a majority of the students exchanging answers and finding out what was right, thus, they weren't actually putting effort in, they were simply trading answers. At the end of class, these "corrections" were accepted as a grade. He also gave all the students a chance to retake the test at their own leisure, I am not a 100% sure if the tests were the same, but I am sure they were identical.
Now you see my overall view in regard to this topic, I believe it is common for teachers to go easy on students, causing them to truly not learn, especially in lower grade classes like IEP. The SAT's do a good job at finding out the true knowledge of a student, and how well they work under pressure, key factors in my opinion.