James J. Heckman and Paul A. LaFontaine write (here is the abstract,

the U.S. high school graduation rate peaked at around 80 percent in the late 1960s and then declined by 4-5 percentage points; (2) the actual high school graduation rate is substantially lower than the 88 percent estimate of the status completion rate issued by the NCES; (3) about 65 percent of blacks and Hispanics leave school with a high school diploma and minority graduation rates are still substantially below the rates for non-Hispanic whites. In fact, we find no evidence of convergence in minority-majority graduation rates over the past 35 years.

Note that the NCES is the National Center for Education Statistics, generally considered the official source. Part of the over-estimate of high school graduates comes from counting GED’s.Heckman and LaFontaine say,

Although GED recipients have the same measured academic ability as high school graduates who do not attend college, they have the economic and social outcomes of otherwise similar dropouts without certification. Despite measures of cognitive ability similar to high school graduates, GED recipients perform significantly worse in all dimensions when compared to them (Heckman and Rubinstein [2001]). GED recipients lack noncognitive skills such as perseverance and motivation that are essential to success in school and in life. The GED opens education and training opportunities but GED recipients do not reap the potential benefits because they are unable to finish these activities.

…Not only is most of the convergence in male minority high school completion rates to those of whites due to higher GED certification rates among minorities, but a substantial portion of these credentials is produced in the prison system.

…The estimated graduation rate is biased upward by 7.7 percentage points when GED recipients are counted as high school graduates. The bias is larger for males than females due to high rate of GED certification in prisons among males…Excluding GED recipients lowers minority graduation rates more than majority rates.

From the conclusion:

The decline in high school graduation is important for understanding the recent slowdown in the growth of college attendance and completion and the growing gender difference in college attainment. In the first half of the 20th century, growth in high school graduation was the driving force behind increased college enrollments. The decline in high school graduation since 1970 has flattened college attendance and completion rates…

I think the solution isn’t to try to force more square student pegs through the round academic hole. My hunch is that we should stop trying to make all these kids sit still and learn in traditional classrooms. Go with more hands-on apprenticeships and such.