There are as many definitions of "middle class" as their are people claiming to be members of it.
The fact is that, a generation (or two) ago, it was possible for a HS grad to walk down to the local mill, factory, or construction site after graduating, and by age 25 have a non-working wife, a couple kids, a house, a new car, and regular vacation at the beach. And he could expect to retire in his 50's on a generous defined-benefit pension.
There are a couple pockets in the economy where that still can occur, but they are few and far between, as well as being tenuous, as those jobs tend to come and go.
Those days are not coming back. Period. We live in a global economy, and the employers who funded this lifestyle would go bankrupt in a heartbeat if they tried to compensate their employees that generously.
Today's generation of HS grads (and comparable) will have to work hard - both husband and wife - spend their limited funds wisely, and always strive to get the best job available, even if it means changing jobs every so often. And it will help if you have parents who are reasonably prosperous Boomers, who can help out with the major expenditures and unexpected problems.
The astounding thing is, there are millions of people who are prospering wildly in these uncertain times. Mainly, they are entrepreneurs and investors of one sort or another, and it don't take no college education to do that. It takes balls, initiative, and as Henry Higgins would say, "...a little bit of bloomin' luck." Look at our coastlines and resorts. Developers cannot build multi-million dollar condo's fast enough, there are millions of yachts floating in the bays, 6-figure sports and luxury cars running about, and they are not all owned by geezers - many by people in their 40's and 50's.
I can't figure it out.