When a student in high school starts missing school it should be a clear warning sign to parents and school officials that there is trouble somewhere in the adolescents life and, if not corrected, will lead to bigger problems.
Results of dropping out of school
Without measured rates of truant students dropping out of high school it is difficult to determine how strong the correlation between the two is. Few sources of data are available to measure the strength of this connection. An article from 2008 in San Francisco noted that 75 percent of all chronic truants eventually drop out of school. Chronic truants are defined as students that have been absent with a legitimate excuse from school for 18 or more days of the 180 day school year. 
According to the 2000 US census, high school dropouts average around a 48 percent unemployment rate, much higher than the 29 percent for high school graduates, and the 17 percent unemployment rate for college graduates.  With almost half of high school dropouts being unemployed, they face a high propensity to entering a life of poverty and crime.
Statistics from a 1997 report from the National Center for School Engagement indicates that 41 percent of inmates and 31 percent of adults on probation were high school dropouts without a GED. 
Impact to Society
Truancy has several negative impacts to society. Truants cause businesses to lose money because of youth who loiter and commit crimes that cost businesses money like vandalism and shoplifting during hours where they should be at school. Individuals in society are impacted through higher daytime crime rates. Taxpayers are negatively impacted through having to fund the cost of social services for the families of youth that are repeatedly truant.  Finally, society in general is impacted negatively through loss of the potential of the individual as a highly functioning contributor. The average high-school dropout will end up burdening the social system with over $200,000 in expenses over the course of their lifetime. 
Members of three grand juries in Dade County, Florida reviewed data from over 5,000 cases where the county’s juvenile offenders were involved. Excessive truancy was noted as a trait that most all of the offenders had in common. Between the years 1978 and 1986 the state of New York convicted 85 juveniles of murder. Over half of these juveniles had a history of truancy. Since 2003 over 90 percent of homicide victims in San Francisco have been school dropouts. 
Many states in the U.S. have programs designed to intervene and correct truant behavior when it is discovered. Parent and family involvement is seen as a key to success.  Incentives for the student to attend school are encouraged and consequences for poor attendance should be established. The consequences are usually in the form of fines levied against the parents. 
The city of Camden, New Jersey recently made headlines with their attendance incentive program. The Philadelphia Inquirer reported on the program where anti-truancy education programs are attended by students focusing on conflict-resolution, anger-management, and educational reinforcement.  These students, who range from 9th to 12th graders, will be paid $100 each for attendance during the first three weeks of school. 
While the solutions aren’t easy the costs to society of truancy is high, as are the costs to the student who is missing out on an education. Truancy in high school students is a multi-faceted problem with many causes and solutions that require a good deal of effort to employ.