The lower middle class live a comfortable life. They hold white-collar jobs that don't require manual labor. They have less education than the upper class, and have to continue to work for what they have.
The working class have jobs that require labor, sometimes these jobs have a higher pay than lower middle class jobs. They are called " blue collar" workers and have less prestigious jobs.
The underclass are people who have had a history of unemployment and poverty throughout their families generations. They work only sometimes at undesirable jobs. They rely on government assistance.