How has America not changed in the last 100 years, in terms of class structure?ex. people born into lower classes generally have a tougher time...

In addition to the example you mention of education, I
would point out two ways in which the US has not changed in terms of
class.

First, the lower class is typically those who work
in unskilled positions.  People who are poorest in the United States are typically those
whose jobs do not take much in the way of education or training.  They work as roofers
or landscapers or maids in hotels.  They work at low-paid jobs in retail.  The fact that
low-skill jobs pay poorly is something that is the same as it was 100 years
ago.

Second, many people in the lower classes are
immigrants.  One hundred years ago, there were many immigrants from Southern and Eastern
Europe.  Today, the immigrants are often from Latin America or Southeast Asia.  However,
in both cases, many of the immigrants make up the lower
class.

So, the class structure is similar to what it was
100 years ago because many of the poor are immigrants working in unskilled
jobs.