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?

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

In a controlled experiment, in which there are two groups with similar subjects, the scientists or research must manipulate one of the variables to test the influence of this variable in another. This implies, if the school principal wants to know whether natural light affects classroom learning, he needs to manipulate the rate of natural light.

Indeed, to be a valid experiment the principal should allow one of the groups to be in a room without natural light and one to be exposed to natural light. In this way, he can compare effectively the test scores. According to this, to be a valid experiment, the principal should introduce adjustable blinds (option B) because in this way he can manipulate the rate of natural light which is one of the main variables in the experiment.