Read this excerpt from a passage.
In 2010, a research team at the University of Minnesota began a three-year study of later start times at high schools in three
states. They compared schools having earlier, more traditional start times with schools starting at times that correspond better t
teens' circadian rhythms. Not surprisingly, the results, published in 2014, showed that some positive things happened at the
schools with later start times. Students earned higher grades in core subject areas. They performed better on achievement tests
And there were fewer absences and tardy arrivals. The research team reported other benefits associated with a later school sta
time (which means more sleep for teens).
What was the cause associated with the positive effects researchers discovered at the schools?