Gwinnett County school officials said Monday they were pleased by the increase in the district's graduation rates, but say they need to do more to prepare students for careers and college.

Gwinnett's four-year graduation rate for the class of 2015 rose by 3 percentage points to 78.1 percent, according to data released by the Georgia Department of Education. The Gwinnett School of Mathematics, Science and Technology, a public charter school that typically ranks among the best statewide academically, posted Gwinnett County's highest graduation rate with 98.9 percent.

“It is not enough that just more of them are graduating in four years … we have to ensure that they are better prepared for college and the workplace,” Kevin Tashlein, Gwinnett’s associate superintendent for school improvement and operations, said in a news release. “That is our ultimate goal.”

Gwinnett last school year converted five of its high schools — Central Gwinnett, Lanier, Meadowcreek, Shiloh and South Gwinnett — into college and career academies. Four of those five high schools had higher graduation rates, with the biggest increase at Meadowcreek, where the rate rose from 52 percent to 68.5 percent. Shiloh High School’s graduation rate declined from 74.1 percent to 72.9 percent.

Tashlein said Gwinnett is studying what is working well in schools and use that to improve student performance elsewhere.