This is true. However, I can tell you that the students we are talking about do extremely well at Starkville High School, and at any other one to be honest.
Adding that the students we are talking about have gotten to the point where most of them are close to perfect scores as it is. You can count on them in your proficiency number.
Not sure how you would compare students who are similar to yours by anything other than the scores they made before. If your kid hasn't taken EOC, then you have no way to know where your kid is other than his or her 8th grade scores. This is problematic since you are using the thing you want to get insight into to try to get insight. Guess you could report aggregate 8th grade scores to what those same students did on EOC, but I'm still not sure what this is really telling you. Students who do well in 8th grade did well in high school. Students who didn't do well do not. Not a surprise.
The biggest thing that would be helpful and also easy to collect (ignoring politics or regulatory issues related to tying identifying information to test scores) would be scores grouped by socioeconomic status and parental status (e..g, married, divorced, never married, employed, unemployed, highest level of education, etc). But I can think of lots of data that would be nice to have if I ran the world. IQ scores and proficiency scores from before or right after kindergarten, 4th, 8th, and 12th grades would be interesting. Hell, I'd throw in BMI, height, and race and anything else that can easily be measured, even if it might only be of interest to researchers and not parents. And parental IQ if I was king for a day.
But being realistic, I think what decile the household income of the child's primary residence falls in would get you 85% of the way there without having to do anything other than have all households fill out the same forms required to qualify for free or reduced lunch.
Which again, may not be politically easy, particularly if parents don't want to provide that info (which I certainly wouldn't want anybody at the school knowing my financial info), but would be really easy data to compile ignoring that.