Full kids listen to the teacher and worry about whether they are going to pass tests.
Hungry kids listen to their growling stomachs and worry about where the next meal is going to come from.
Rich families tend to do fine by themselves because money isn't making them worry about where the next meal is going to come from or whether they will have electricity by the end of the month, or even a roof over their head. Poor families do have to worry about these things, hence the extra need for help and support.