A psychologist is describing the different personality disorders. When she comes to avoidant and schizoid personality disorders, the students look puzzled. How will she distinguish these two personality disorders?

The main difference is that the avoidant personality tends to crave relationships but is afraid of rejection, thus the name avoidant, whilst the schizoid personality generally doesn't crave relationships.

Explanation:

Both disorders are part of the Personality Disorders which are divided into clusters:

Avoidant: it belongs to cluster C, characterized by a general feeling of anxiousness as well as being perceived by others as withdrawn. Schizoid: it belongs to cluster A, characterized by a difficulty to relate to others and perceived as weird for certain behaviors, for example.