Final answer:
The social worker should first assist the son in accepting his mother's praise, reinforcing positive interactions and addressing possible underlying reasons for his difficulty in accepting compliments.
Step-by-step explanation:
In the context of a social work session addressing frequent conflicts between a mother and her 15-year-old son, when the son dismisses his mother's praise, the social worker should prioritize reinforcing positive family interactions. The most appropriate first action would be to assist the son in accepting his mother's praise. This can be achieved by facilitating a dialogue that acknowledges the son's contributions and helps build his self-esteem. It might also be helpful to explore, in a supportive way, why the son might find it hard to accept praise, considering broader sociological factors such as generational differences, historical parenting norms, and economic backgrounds, which may affect family dynamics and individual behaviors.