Did This “Study” Actually Exist? The Answer
As far as I can tell, there does not seem to be a control group in the study. In addition, there were several dietary changes and they may have focused on on irrelevant ones. Changes in micronutrients sound more plausible than changes in food additives. After all, the students would later go home and eat Twinkies but the school meal might have been their only meal with real food. One of the authors was later involved in a study that did have a control group and found that micronutrients are important.
I won't more than mention that, if I recall correctly, the use of mind-altering chemicals was dropping rapidly in New York City at the time. Maybe second-hand toke had an effect.
I have started a log at Ask for Evidence but their system appears to be down now.