Parents aren't necessarily in the clear when their children walk across the stage to claim their high school diplomas, according to a study by the University of Michigan's Institute for Social Research.

About 20 percent of students who were doing well as high school seniors were not meeting their stated or expected goals at age 26, according to a study called "Monitoring the Future".

"What's scary is that it's unpredictable," says John Schulenberg, Ph.D., professor of developmental psychology at the University of Michigan in Ann Arbor, and the study's lead researcher. "We used to think that if things were going well in high school, they'd continue to go well."

The ongoing study analyzed data from more than 2,900 young people initially surveyed as 18-year-old high school seniors, and again at ages 21 to 22, and 25 to 26, to assess whether respondents were thriving in key developmental areas.

By age 26, the study showed 29 percent were not financially independent, which they defined as supporting themselves alone or with the help of a spouse. Another 21 percent had strayed from previously stated educational goals, which included graduating from two-year or four-year colleges.

Transitioning to adulthood may be more difficult in the U.S., says Schulenberg. American youths lack institutional structures such as apprenticeship programs, which guide young Europeans in their careers.

But there is a flip side to the U.S. story: Many young adults who feel stifled and unhappy in high school thrive on their new freedom and responsibility after graduation, according to Schulenberg.

The study did not track how parental influence affected post-high school success.