Maine ranks 15th in the nation for high school students graduating on time, with 85 percent of students who entered the ninth grade in fall 2008 earning their diplomas in 2012, above the national average of 80 percent, a new report found.

State education officials, however, urged caution in interpreting the report being released Monday, saying that the graduation rate is just one part of gauging the success of schools and the report glazes over a worrisome trend in Maine.

The national graduation rate hit its highest level at 80 percent in 2012, according to the report by organizations focused on education, including America’s Promise Alliance, a group founded by former Secretary of State Colin Powell.

A separate state analysis found that of 133 schools, 73 improved their four-year graduation rate from 2012 to 2013.

The Maine Department of Education found York County had the highest graduation rate at nearly 90 percent, and Androscoggin County had the lowest at nearly 78 percent.

But despite placing well among other states in the national report – though low-income students lagged behind other students as they did around the nation – state officials cautioned there are other issues that must be addressed.

“I’m encouraged by anything that improves graduation rates in Maine. But I can’t just leave it at that. It is so much more our goal to have students prepared for careers and college,” said Education Commissioner Jim Rier.

A third of Maine students who go to state colleges must take remedial courses to brush up on basics, he said.

In the 2013 school year, 37 percent of Maine students graduated without meeting state proficiency standards in math or reading.

Unlike other states, Maine does not require its students to meet its proficiency standards to get a diploma.

However, a system that will take effect in 2018 will change that, requiring schools to award diplomas based on students’ mastery of new learning standards still being developed.