Music is important to the human brain. We are hard wired to recognize pitch, rhythm, and intonation. A person with no musical training at all can detect an out of tune note. This seems to be because verbal communication uses these same elements, and verbal communication is a critical survival tool.
Music makes the brain grow. Childhood music lessons actually enlarge portions of the brain. German researchers found that the brain area used to analyze musical pitch is an average of 25% larger in musicians. The younger the musical training begins, the larger the area. 
Students in music generally test higher. One ten year study from Dr. James Catterall analyzed data from over 25,000 students from the U.S. Department of Education. This study showed that students involved in music generally tested higher than those who had no music involvement, without regard to socioeconomic level. Test scores were higher in standardized test, such as the SAT, but also in reading proficiency exams.  Another study by Dr. Lewis Thomas of 7,500 university students revealed that music majors scored the highest reading scores among all majors, including english, biology, chemistry, and math. In the same study, 66% of music majors who applied to medical school were admitted, the highest percentage of any major, including biochemistry (44% admitted). 
 Nature, April 23, 1998.
 Dr. James Catterall, UCLA, 1997.
 The Comparative Academic Abilities of Students in Education and in Other Areas of a Multi-Focus University, Peter H. Wood, ERIC Document No. ED327480. The Case for Music in the Schools, Phi Delta Kappan, February, 1994.