The answer is: This is just one example of the benefits schools get from offering music classes to their students.
The paragraph is making an argument in favor of music as part of a student´s education as an element that can be determining in graduation efficiency rates. In order to complement this argument, the best way is to add that this is only one of the many benefits that music would have on students´ education, therefore implying that there are other benefits that makes the argument even more persuasive and solid.