I'm surprised I even have to explain this here but testing for basic language proficiency is not the only thing these types of tests are for. They test elements of writing, grammar, critical analysis, and vocabulary that students are still learning.

Unfortunately, I couldn't find any easy way to get example questions - they're all locked behind a login that requires student id.

Furthermore, this isn't entirely an ESL issue - according to the article, scores for African-American students were the lowest, and they're obviously native speakers. So we would need more information to figure out the origin of this disparity.

One final point - these numbers are the percentage of students who scored above a threshold, NOT their average scores. All of the scores for every ethnic group are likely on something like a normal distribution, shifted to the right or left. Of the groups who performed below the standard, it's likely that the majority of them performed very close to the standard even if they were just below it.