First off, I think the "middle class" and "working class" can be the same thing. The "working poor" are another segment. "Middle class" is actually a socio-economic term. I tend to believe it is all defined by income. The middle class have always been the backbone of the country, that is, until this current administration took over. To me, someone middle class generally is better educated, can afford to own their own home or condo, owns a car (maybe two), can afford to shop for modest luxuries like a TV, cd/dvd player, cell phones, new clothes, etc...They probably take a decent vacation every year, own a couple credit cards and enjoy the usual trappings in life. They keep the economy moving with their purchasing power. The "working poor" are generally living paycheck to paycheck, are renters, may not own a car or qualify for a home or credit cards and may not have a formal education beyond a couple years of high school. There are certainly exceptions to all of this. For example, some "students" may be in the "working poor" but only temporarily, until they finish their education and move on. They are also paying for an education, which is an investment.There are also those in the middle class who do not choose to own a home or take vacations or spend money on the usual trappings...but they are still middle class.
There are also levels of middle class...lower and upper middle class...but generally the middle class are those people who have a certain degree of economic independence but not a lot of social influence or power, unless they act as a group.