Professor castillo is studying the aggression of preschool children during recess. he has several observers recording the children's behavior, but none of them are allowed to interfere with the children at play; they simply record what they see. professor castillo is using:

Professor Castillo is likely using naturalistic observation. Naturalistic observation is a research method in which is employed in order to observe a specific object or subject that are within the natural environment in which Professor Castillo is engaging in based on the scenario.