"Are American children from lower middle, lower, and impoverished socioeconomic backgrounds doomed educationally and socioeconomically to very dire circumstances with extremely bleak outcomes?"
I think many are however there always are exceptions. Some children grow up to play or major sports teams or become successful rappers, singers, actors, or entertainers. Some will join the military to escape their circumstances and go onto make something out of their lives. There are also those who will get academic scholarships and there will some who learn a trade such as bricklayer, electrician, auto mechanic, carpenter, welder, or truck driver. All of these choices can lead to having a lower-middle class life and beyond if there is a "plan".
There is no sin in being born poor or in an impoverished area. It's making bad choices and not having goals that keeps one down. Avoiding gangs, drugs, pregnancies, associating with known criminals, and stealing are easy traps to fall into especially if one's parents aren't role models or at least showing them a potential future they could have.
Being young generally means being immature. When you're young you only think about right NOW. A 14 year old can't envision being 18 and graduating from high school. That seems like a lifetime away!
Therefore if one of their friends tells them they a have way to make a few hundred or thousands of dollars doing something illegal that sounds better than delivering newspapers or wearing a uniform and working at McDonalds.
The promise of fast easy money keeps many impoverished youth from having long-term goals and working steady to achieve them. This also explains why there is a higher incarceration rate for them.
"Vision without action is merely a dream. Action without vision just passes the time. Vision with action can change the world." - Joel A. Barker
The first step is a person has to decide to get out of poverty.
Believe it or not some people don't want to move away from impoverished areas. Others who have gotten out continue to come back and associate with those they grew up with.
One should examine all of their legal options and then create a plan. The bear minimum would be to finish high school, join the military or get a civil service job. Even learning how to sell products and services for a company in an entry level position can turn things around. If one has a minimum wage job and a friend who also has one they become roommates and MOVE to a nicer area.
Networking can be a goldmine!