I'd like to read the actual study. While I agree that a varied and moderate diet is good for everyone, children included, of course you have to look closely at someone who is employed by the USDA. Having had first hand experience with the USDA's ag cotton groups, I can tell you they are not beyond manipulating data and interpretations for their own purposes. If this researcher is working the same way, then the claims of the vegan groups may actually have some merit.
The other questions are in regards to the actual study. Obviously, the first question is the evaluation of the children's performance which seems somewhat subjective and prone to bias. The second is that these were poverty stricken kids who are probably severely lacking in basic nutrition and caloric intake. Certainly adding meat into any of their diets would help replenish lost micronutrients that make a difference in function. Would the same be true of US children, who are getting progressively more obese with hypercaloric diets?
Finally, in India you have perhaps the world's largest populations of vegans anywhere on the planet. Coincidentally, you also have a lot of poverty as well. Yet the country produces some of the brightest minds in the world in engineering and medicine. Apocryphally, what we could conclude is if they added meat to their diets of their children in the last millenia of veganism, they would have ruled the world by now. You can see where I am going here.
I am a meat eater and proud of it. But, in this case, I think Lou and perhaps you John, are seeing what you want to see. I imagine Dos, who is a vegan, would have a more impassioned response to this study.