Dr. murphy studies a cohort of schoolchildren and follows their progress through college. dr. murphy is most likely a:

Dr.Murphy is most likely a developmental psychologist.

Developmental psychologists study how and why individuals change and progress throughout their lifespan in terms of their social, moral, emotional and cognitive functions. If Dr.Murphy is studying  cohort of school children and following their progress through to their college years, he is tracking their development and progress through their growing years in terms of their moral, social, cognitive and biological growth.

Developmentalist. Here the approach to teaching and learning is from a constructive and developmental framework. In this process knowledge is considered as a construction of interaction of mind with the world. Here the learner is wanted to be creative and critical.