PORTLAND — Maine’s fourth- and eighth-graders scored better than the national average on math and reading assessments, according to a study released Thursday. But the report also showed there was no improvement from the last assessment.

Nationally, students performed better than they did when the tests were first given in the early 1990s, but the vast majority still fail to demonstrate solid academic performance, according to the National Assessment of Educational Progress.

In Maine, 47 percent of fourth-graders and 40 percent of eighth-graders scored at or above the proficient level for math, compared with 42 percent and 35 percent nationally. On reading, 37 percent of fourth-graders and 38 percent of eighth-graders were proficient or better, beating the national average by about 2 percentage points.

Maine’s performance was the same as it was in the last assessment two years ago.

“Maine is above average but not improving,” said Samantha Warren, spokeswoman for the Maine Department of Education.

Gov. Paul LePage, a Republican who credits education for lifting him out of poverty, has criticized the public education available in Maine. He has clashed with Democrats over some his school-improvement plans, including an expansion of charter schools. Democrats have criticized his A-to-F ranking system for schools and teacher evaluations.

Maine officials noted some caveats in the assessment. For example, the assessment featured a small sample, roughly 3,000 out of the state’s 185,000 public school students in those grades.

Overall, Maine ranked 14th among states on the assessment. But Rachelle Tome, the state’s chief academic officer, remembers when Maine ranked at the top when she was a fourth-grade teacher.

“We’re just sort of staying stagnant,” Tome said.

And while optimists will point out that Maine is better than average, it’s important to note that more than half of students were not proficient in the subjects, she said.

“We want all students to be college and career ready, not just half of them,” she said. “I want that doctor or auto mechanic to have the skills that they need.”