The main theme of "An Elementary classroom in a Slum" is inequality. Throughout the poem the author Stephen Spender paints a picture of children too sickly and hungry to focus on their studies. Spender politically believed in socialism and therefore had very strong beliefs about fairness and equality among all people. The situation he describes shows that this classroom in an impoverished area is certainly not treated fairly.
Through much of the poem Spender expresses frustration over what he believes is a futile situation (making students learn when all they are thinking about is survival). For example, he describes the classroom window and map on the classroom wall as a "catacomb." Spender also describes Shakespeare as "wicked" for unfairly giving these impoverished children hope for a better life with his stories while adults with power are doing nothing to help their situation.
Spender starts his final stanza by placing this inequality on the backs of "governors, teachers, inspectors and visitors" who could potentially solve this situation. The poem ends on a much more positive note stating that if students can be given the proper necessities (food, medical care, etc.) their education will set the children free.