The nation’s graduation rate rose to an all-time high in 2016, according to data released Monday. (Gabriella Demczuk for The Washington Post) The nation’s graduation rate rose again to a record high, with more than 84 percent of students graduating on time in 2016, according to data released Monday by the U.S. Department of Education. That is the highest graduation rate recorded since 2011, when the Education Department began requiring schools to report rates in a standardized way. The graduation rate rose by nearly a percentage point from 2015 to 2016, from 83.2 percent to 84.1 percent. It has risen about 4 percentage points since 2011, when 79 percent of students obtained a high school diploma within four years. [Nation’s high school graduation rate reaches new record high] All minority groups saw a rise in on-time graduation rates in 2016, but gaps persist. Only 76 percent of black students and 79 percent of Hispanic students graduated on time, compared to 88 percent of white students and 91 percent of Asian/Pacific Islander students. The Obama administration considered the rise in graduation rates among its most important achievements in education, but experts have cautioned those rates can be a poor measure of how prepared young people are for work and higher education. Even as they are graduating at higher rates, students’ performance on the National Assessment of Educational Progress, a test of reading and math achievement, is unchanged or slipping. [U.S. high school seniors slip in math and show no improvement in reading] There are other reasons to be skeptical. Some districts have used questionable methods to get students to the finish line, including softening grading scales and using credit recovery programs, which allow students to take abbreviated versions of courses to make up for failing grades. In Maryland’s Prince George’s County, officials are investigating accusations that administrators inflated grades so students could graduate. D.C. Mayor Muriel Bowser has begun an investigation into allegations that Ballou High School students were allowed to graduate despite being chronically absent. [D.C. plans probe of Ballou High School following