It's a complete load of bunk.
DUmmie is citing this six-month-old "article" on school homelessness. This is nothing more than a blog post from some Commie statist organization run out of the UCLA campus. This particular bit comes from Noel Brinkerhoff, a Leftist kook activist masquerading as a journalist. The "article" gets its "data" from another activist group, who in turn got their "data" from yet another activist group (.pdf warning), who are masquerading as a government entity. THEY got their "data" from the Department of Education, allegedly, though they also apparently collect and compile the "data." No conflict of interest there or anything. 
All of this BS centers around the McKinney-Vento Homeless Assistance Act, passed back in '87. The idea at the time was to find ways to help out families who turned out homeless, ostensibly through no fault of their own, all part of that "do something!!!" legislation on homelessness after the Left humanely closed down all the insane asylums and sent all those people out into the streets with a prescription and nothing else. Anyway, what's important here is just exactly what the definition of a "homeless student" is:
Clary then worked with national advocates to ensure that the protections afforded to homeless children by the Illinois statute were incorporated into the McKinney Act. That point, the McKinney Act was amended to become the McKinney-Vento Act. That Act uses the Illinois statute in defining homeless children as “individuals who lack a fixed, regular, and adequate nighttime residence.” The Act then goes on to give examples of children who would fall under this definition:
(a) Children sharing housing due to economic hardship or loss of housing;
(b) Children living in “motels, hotels, trailer parks, or camp grounds due to lack of alternative accommodations”
(c) Children living in “emergency or transitional shelters”
(d) Children “awaiting foster care placement”
(e) Children whose primary nighttime residence is not ordinarily used as a regular sleeping accommodation (e.g. park benches, etc.)
(f) Children living in “cars, parks, public spaces, abandoned buildings, substandard housing, bus or train stations…”
Well, the definition problems here are a mile wide. First of all, the definition of "nighttime residence" is very intentionally left wide open to any interpretation anyone wants it to be, so much so that at least back in the mid-'90s, I was aware of many cases in which "latchkey kids" who lived in certainly adequate, and often quite nice, homes were deemed "homeless" because they were latchkey kids and there wasn't a parent in the home between 3:30 and 5:00 in the afternoon, so that wasn't "adequate housing" for the hour and a half that those kids watched cartoons in the afternoon, and thus the school qualified for a grant for each of those "homeless children." And of course there's a bit of a problem with defining everyone who lives in a trailer as being "homeless." Sure, there are much better housing options out there than trailers, but plenty of them are plenty nice and certainly adequate housing; my ex-wife grew up in a trailer and her mother still lives in that same trailer to this very day, and while it's not marble floors and Swarovski chandeliers, it's very comfortable housing for her and has been nicely modified to accommodate her in her wheelchair. And one of the biggest middle-fingers I've seen out of this was at least one relatively wealthy school district who were taking (e) to a ludicrous extreme by saying that kids who played basketball and football and were in the band and whatnot after school were using a "nighttime residence not ordinarily used as a regular sleeping accommodation," because it was after school hours and sometimes in the winter basketball practice isn't over until after the sun goes down. Cha-CHING! Every kid who does some after-school activity is suddenly "homeless" and qualifies for a grant to the school.
This whole idea about helping out whole families who have lost their homes started out as a noble enough idea, but, surprisingly (not!), it pretty much immediately became a federal giveaway program restrained only by the scrupulousness of local school administration officials in their own little fiefdoms who could (and still can) pretty much create their own definitions of who qualifies for these federal grants, and of course, the more students who qualify, the more gravy comes in on that federal train. So of course these numbers are going to seem a mile high most particularly in tough times when school districts have to get "creative" on getting their funding. And the advocacy groups who are the fed's "point people" certainly have every interest in seeing as many people as possible who qualify, so they're going to push these numbers as high as possible.
So, in summary, it's a BS number made up by a BS advocacy group acting at the behest of the federal government, and then repeated ad nauseum by a bunch of other BS advocacy groups as if it were fact, and then wept over by a bunch of liberal suckers who eagerly believe this crap because it fits their bigoted Leftist stereotype.