President Barack Obama is taking on the challenge of increasing the United States’ all but stagnant economic mobility.

He wants, he said in Tuesday’s State of the Union Address, to both “strengthen the middle class” and “build new ladders of opportunity” into it. His modest plan — modest so that it does not need the congressional approval he’s unlikely to receive — includes raising the minimum wage for federal contract workers and offering workers a new workplace retirement savings account option.

It’s a nice start. But nowhere near enough.

The United States’ sluggish economic mobility is not new. According to a paper recently published by academics at Harvard University and the University of California, Berkeley, it has been mediocre for those born in the 1970s, and it is just as bad for those born 20 years later.

So what’s different now? Two things. First, the fast-growing rate of income inequality has left the rungs on the mobility ladder further apart than ever before. The top 1 percent of earners, as Paul Krugman recently noted, saw their incomes increase by 182 percent between 1979 and 2012. The next 4 percent saw a gain of just under 52 percent.

The ever greater amounts of money earned by the highest tier allows them to buy privileges that all but ensure their children can remain at the top. Upper-income families inhabit a world where private schools charge annual tuition totaling only a few thousand dollars less than the median household income, and pricy tutors, extracurricular activities and private college counselors ensure their children will retain their privileged status. Even the best and most exclusive suburban public high schools can’t offer these advantages.