Dr. Land conducted a research study in a preschool where he asked teachers to change their typical ...

Dr. Land conducted a research study in a preschool where he asked teachers to change their typical procedures so that he could test his hypothesis that the amount of unstructured time (free play) structure in a day affects the amount of unruliness that children display. Teachers systematically varied the amount of free play each day for a month, and Dr. Land's research assistants recorded the amount of unruliness children displayed each day. This study would best be described as a
A) correlational study.
B) laboratory experiment.
C) field experiment.
D) self-report study.