Mark Riddell arrives at federal court Friday in Boston, where he was scheduled to plead guilty to charges in a nationwide college admissions bribery scandal. (Associated Press)

An expert test-taker who admitted posing as wealthy high school students to take their ACT and SAT exams pleaded guilty Friday in connection with a college admissions scheme that has also ensnared dozens of parents -- including Hollywood celebrities and corporate executives.

Mark Riddell, 36, pleaded guilty in a Boston federal courtroom to conspiracy to commit mail fraud and conspiracy to commit money laundering and agreed to forfeit $240,000, the Los Angeles Times reported. Prosecutors allege that more than 50 parents paid up to $25 million to middleman William “Rick” Singer to guarantee spots for their children at elite universities.

“I can make scores happen,” Singer told one parent of Riddell’s ability to boost test scores, according to wiretapped conversations quoted in the FBI affidavit. “And nobody on the planet can get scores to happen.”

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For $15,000 to $75,000 per student, Singer brought in Riddell to take tests in their place or correct their responses afterward. Riddell, of Palmetto, Fla., accepted cash payments from Singer and flew to testing centers in Vancouver, Canada; Houston and West Hollywood, Calif.

“I want to communicate to everyone that I am profoundly sorry for the damage I have done and grief I have caused those as a result of my needless actions. I understand how my actions contributed to a loss of trust in the college admissions process,” Riddell said in a statement last month after the charges were announced.

"I am profoundly sorry for the damage I have done and grief I have caused those as a result of my needless actions. I understand how my actions contributed to a loss of trust in the college admissions process."
— Mark Riddell, 36, who pleaded guilty to conspiracy charges

Among the tests allegedly rigged by Riddell -- a Harvard graduate and the former director of college entrance exam preparation at a Florida prep school -- was an SAT exam for the daughter of actress Felicity Huffman, according to the paper. Huffman pleaded guilty Monday to fraud conspiracy. She paid Riddell $15,000 to correct her daughter’s answers, prosecutors said.

Around 20 parents charged in the scheme paid Riddell to fix their children’s tests, according to prosecutors. He was paid around $10,000 per exam, prosecutors said, USA Today reported.

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Another was for the son of David Sidoo, a Canadian businessman and former Canadian Football League player, according to the Times. In 2011, Riddell took the SAT for the student and scored a 1670, enough to gain admission to Chapman University in Orange, Calif. Riddell was also paid to take the student's graduation exams as well.

Riddell is scheduled to be sentenced July 18. He faces up to 20 years in prison and a $250,000 fine. But prosecutors have recommended between 33 months and 41 months in prison.