A school principal wants to observe if natural light has an effect in the classroom learning. The principal randomly chooses two groups of students of the same age and grade, and places both groups in rooms on opposite sides of the school, one facing east and one facing west, during a 10 am class. The test scores of both classes are compared at the end of the semester.

How could this observation be changed into a valid experiment of the effects of natural light?

Question

A school principal wants to observe if natural light has an effect in the classroom learning. The principal randomly chooses two groups of students of the same age and grade, and places both groups in rooms on opposite sides of the school, one facing east and one facing west, during a 10 am class. The test scores of both classes are compared at the end of the semester.

How could this observation be changed into a valid experiment of the effects of natural light?

snowflakelove15 · Answer

A.	by including classrooms facing north and south
B.	by introducing adjustable blinds in each classroom
C.	by tinting the windows in both classrooms with the same film                           		D.	by introducing adjustable light fixtures in each classroom

mww · Answer

Tricky one. 

I think B let's you test the natural light directly by introducing possible negative control.
By varying the amount of natural light that comes through, you eliminate the related variable of 'classroom' location and just focus on light.