If you're going to quote studies, you should cite then. Then we can pick apart what "mobile" means to your ivory tower researchers, which is almost definitely not "traveling the world as a healthy, happy, family unit."
Diplomats travel with their families. Employees of multi-nationals travel. US military travel. At least that last group (i.e. their kids) I know does better than average.
It seems to me that their survey intermingles two very different groups – the larger group, those who moved due to extreme financial insecurity (who would do MUCH worse), and those who moved under "positive" circumstances.
Diplomats travel with their families. Employees of multi-nationals travel. US military travel. At least that last group (i.e. their kids) I know does better than average.