Carroll County was the only school system in the state with a graduation rate of 95 percent or higher in 2014, according to data released Tuesday by the state Department of Education.
Meanwhile, Maryland's high school graduation rate increased for the fourth year in a row, with just more than 86 percent of high school students earning their diploma on time this past school year.
Carroll County Public Schools Superintendent Steve Guthrie said there are three reasons for the county's unparalleled success.
"We have committed staff; we have dedicated students; and we have a supportive community," Guthrie said. "These three are essential for any school system to be successful. If you don't have them all, you can only get part of the way there."
Federal law mandates that graduation rates greater than 95 or dropout rates less than 1 percent can't be made public because such small margins could allow those who didn't graduate or dropped out to be identified.
The graduation rates are measured using a cohort system, implemented in 2006, which tracks all children who enroll in public school from the point they enter in ninth grade to the time of graduation, said Greg Bricca, director of research and accountability for CCPS.
For decades, the state used a leaver system, which measured the number of graduates per year against the combined number of graduates and dropouts, The problem with that system is the possibility of someone being counted twice for dropping out, Bricca said.
"If someone drops out in 11th grade then re-enrolls and then drops out again during senior year, that one person would be accounted for twice," Bricca said.
The most encouraging news in the data is that Maryland students from all minority groups accounted for are making gains. The graduation rate for African Americans rose from 76 percent to 81 percent over the past four years. Even greater numbers of special education students, who have had difficulty getting a diploma in the past, are finding their way to the stage each June.
Only students who are learning English — often the state's most recent immigrants — are losing ground, according to the data.
Baltimore City remains the school district with the lowest graduation rate in the state, but its progress over time has exceeded nearly every district.
Two Eastern Shore counties — Somerset and Dorchester — made significant progress amid lower income populations. Dorchester County's graduation rate rose 5 percentage points to 87.9 percent, while Somerset rose 8.5 percentage points to 86 percent.
Only Howard, Caroline, Washington and Frederick counties saw decreases; most were slight.