What kept some african americans who could read and write from passing litercy tests?

The thing that kept some African Americans who could read and white from passing the literacy test was because the test they had to take were very difficult. The African American reading and writing levels were average, they know how to do basic writing techniques and know how to read, but the tests that they were given were in a higher level than they knew. For example, it's like giving a 1st grader a 10th grader test, they wouldn't know how to do it because it would be very hard, that is what the African Americans had to go through when they were given the literacy test. If they were to be given a test that was in their level. they would pass it, but since the tests were extremely hard, it was impossible for them to past the test since there were stuff in the test that they never heard of knew of.