Follow the money...
As a successful "high-school dropout"--I took the GED at 17 and enrolled in college--I was appointed to a committee that had the mission to discover the causes of the high dropout rates in our city.
What a shock it was for me to learn that dropping out of High School to begin college "costs the school district federal funds" and "lowers the graduation rate" which "reflects poorly on the district". So the committee voted 9-to-1 to recommend raising the legal dropout age to 18. They have not succeeded in persuading state legislators, yet, but in 1998, the dropout definition was changed to count "students who leave high school without graduating to enroll in Community College or a GED program."
In NC, teens can take the GED when they are 16 years old. There are two ugly caveats: (1) The state law requires the student to drop out of High School officially, prior to registering to take the exam (link); and (2) Officially withdrawing also means losing the legal right to drive. If teens under the age of 18, they cannot drive unless they have a diploma or are enrolled in High School.
Some resources on success rates, etc of GED candidates are available at this link.
Specifically, vpintheak, these ridiculous restrictions and laws have been put in place to keep public school enrollment levels overly inflated. Warm bodies mean cash, jobs and pensions. Furthermore, there is a genuine concern among well-meaning liberals that kids must have a minimal level of education in liberalism before entering the working world and/or they hold a genuine belief that public schools provide good educational experiences to any child who wants to learn.
Yikes.
What a shock it was for me to learn that dropping out of High School to begin college "costs the school district federal funds" and "lowers the graduation rate" which "reflects poorly on the district". So the committee voted 9-to-1 to recommend raising the legal dropout age to 18.
***Notice what is missing here. The folks who are establishing policy for our children do not have the child's best interest at heart. They're more interested in keeping the gravy train rolling.