In today's budget-strapped schools, there is usually only one psychologist per district. The psychologist’s job is basically to test students for learning disabilities to see if they need an IEP (Individualized Education Program). Unfortunately, the psychologist does not really treat anything and does very little follow up. He or she simply tests the student, usually in a couple of hours, and then makes a recommendation. School site special education teachers proceed from there to design the student's modifications. However, that does not mean it is not an important function. The psychologist is needed to make sure the child gets the needed interventions.
To learn more about IEPs, read here: