The only way this can be true is if the '10%' figure equals the proportion of illegal immigrants in the study that have school-aged children.
There are several school districts here in Arizona whose student population is composed largely (one-third or more) of illegal aliens.
Fix-the-math bump.
The Texas school system has been groaning under a mass of Mexican children for 20 years.....the old schools built for the Boomers are bulging again, and the Houston school system is having both to consolidate schools in order to abandon decrepit buildings from the 50's and build new schools. (And of course, they've just HAD to build themselves a big new administrative complex at the same time! -- but that's another issue.)
My friends in suburban Atlanta tell me the same story -- kids who shouldn't be here, swinging from the rafters and jamming both the schools and hospital ER waiting rooms.