A longtime Memphis educator who helped teachers cheat on certification exams over a 15 year period was sentenced Monday to seven years in federal prison.

Clarence Mumford, 59, slumped in his chair and lowered his head several times during his sentencing hearing in Memphis federal court. He pleaded guilty in February to arranging for people to take Praxis certification tests on behalf of aspiring teachers in Arkansas, Mississippi and Tennessee.

Teachers paid Mumford up to $3,000 each to hire ringers to take reading, writing, math, physical education and other exams on their behalf. That fee included fake driver’s licenses Mumford made for the test-takers, who showed them to proctors at examination centers.

The teachers then used the passing scores to get jobs in public school systems.

Mumford, a former guidance counselor and assistant principal in the Memphis City Schools system, paid the test takers hundreds of dollars for each test. Still, federal prosecutors said he made $120,000 in the scheme, which ran from 1995 to 2010.

Prosecutors called the case unique because of the length of the scheme and its wide-ranging consequences. Prosecutors said the scam affected thousands of public school students who ended up being taught by instructors who never qualified for their positions. Some teachers involved in the scheme had repeatedly failed the tests on their own.

Teachers with false qualifications also ended up landing public school jobs for which honestly qualified teachers had applied.

“The impact of having these unqualified teachers in our schools is immeasurable,” Assistant U.S. Attorney John Fabian said.

Mumford’s wife, cousin and friend each spoke positively about Mumford, saying he was a caring man and thoughtful educator who just wanted to help people before his scheme got out of control.

Mumford apologized to the judge, the Memphis educational community and his church. He said he didn’t have a desire to defraud or cheat anyone.

“I will always regret what I have done,” he said.

U.S. District Judge John Fowlkes said he took that into consideration, but he agreed with the government’s recommendation of seven years in prison partly because Mumford had grown to believe that it was OK to cheat and make money from it.

“This conspiracy was complex. It was deep, lengthy,” said Fowlkes, adding later that money became a “driving force” behind Mumford’s actions.

Mumford pleaded guilty to conspiracy to commit mail, wire, identification and Social Security fraud and one charge of aggravated identity theft. Evidence in the case included pages of photos of fake driver’s licenses made by Mumford.

Educational Testing Services, which writes and administers the Praxis examinations, has said the company discovered the cheating in June 2009, conducted an investigation and canceled scores. The company began meeting with authorities to turn over the information later that year.

At least 12 teachers and test-takers have pleaded guilty in the case. Prosecutors say 18 other people have agreed to court-ordered diversion.

Frances R. Jones told prosecutors that she had been hired on an emergency basis by Amanda Elzy High School in Greenwood, Miss., but failed to pass exams she needed to keep her job. She testified that she paid Mumford $3,000 to arrange for a test to be taken on her behalf. However, the ringer “got spooked” at the testing center and never took the exam, Jones said.

Jones said Mumford sent someone else to take the test for her, but required her to pay $3,000 more. The score was canceled by Educational Testing Services because the handwriting on the test did not match hers, she said, but Mumford kept the $6,000.