North Carolina continues to lead the nation in the number of teachers who have earned certification from the National Board for Professional Teaching Standards, the highest credential in the teaching profession.

The national certification is a rigorous performance-based assessment taking anywhere between one to three years to complete. About 21,500 North Carolina teachers have obtained the credential, with 616 additional teachers earning the endorsement last month. Additionally, 890 board certified teachers in North Carolina obtained recertification.

The Tar Heel State accounts for nearly one fifth — 18 percent — of all teachers nationally who are certified, followed by Florida, with 13,555 teachers. Washington is third, 10,018; South Carolina is fourth, 9,024; and California has 6,755.

“Our state’s students are the winners when their teachers invest the time and effort to meet the demanding standards of national certification,” State Superintendent Mark Johnson said in a press release. “The certification process helps teachers strengthen their practice to be highly effective educators in their classrooms and able instructional leaders in their schools.”

Becoming nationally certified is voluntary, but in North Carolina teachers who are certified receive a 12 percent salary supplement to their regular pay for the 10-year life of the certification. Certified teachers also received eight continuing education credits and can receive two more credits when they are recertified. Out-of-state teachers who are employed in North Carolina can obtain a state teaching license from the State Board of Education if they are nationally certified.