BALTIMORE -- The percentage of students earning their high school diplomas within four years dropped in Prince George's County, while the number of graduates continues to rise in Montgomery County, according to 2011 data released by the State Education Department on Wednesday.

In Montgomery, 86.8 percent of students graduated on time in 2011, up slightly from 86.2 percent in 2010. Black and Hispanic students made the most significant strides -- 78.1 percent to 81.3 percent for black students and 74.2 percent to 75.3 percent for Latinos -- although they were still outperformed by their white and Asian peers.

Across the state, Maryland's four-year graduation rate increased from 82 percent to 82.8 percent.

Finishing on time?
Percentage of public school students who graduated high school within four years:
  2010 2011
Montgomery 86.2% 86.8%
Prince George's 76.2% 74.6%
Maryland 82% 82.8%
Note: 2010 was the first year that Maryland calculated its four-year graduation rate.

But crossing the stage in Prince George's, a number of would-be graduates stumbled. The four-year rate slipped from 76.2 percent to 74.6 percent. And the percentage of Hispanic students graduating on time plunged from 65.5 percent to 57.8 percent.

Duane Arbogast, the chief academic officer for Prince George's County Public Schools, said the district is seeing an increase in immigrant families. Many of the children have had interrupted schooling, and some are entering high school with no experience speaking English.

"We're also really competing against a work climate where, for many kids, it's an opportunity cost to actually attend school," Arbogast said. "They're trying to find full-time jobs to support their families. ... For us to really switch the Latino graduation rate, we simply have to acknowledge that many of these children are working full-time."

Although Montgomery County also has had to grapple with shifting demographics, including an increasing immigrant population, schools spokesman Dana Tofig said there's no secret fix that the district has been using.

"Because of the [tight] budget, we haven't had a lot of new programs, a lot of new initiatives, per se, but we've sort of been consistently sticking with what we think is working," Tofig said. "Graduation rate is the end; that's the ultimate indicator of what we've done from K through 12. If we're seeing growth in that, it means what we're doing is working, though we recognize there are gaps we need to address."

In October, Virginia released its 2012 on-time graduation rate at 88 percent, up from 86.6 percent in 2011. Fairfax County Public Schools' 2012 rate stayed relatively flat at 91.3 percent, the highest in the region. Arlington Public Schools' jumped from 87.6 percent to 89.2 percent, while Alexandria City Public Schools' increased from 79.2 to 81.9 percent.