His mastery made him an invaluable commodity in the college admissions bribery scheme, an SAT and ACT ringer who doctored entrance exams or took the tests on behalf of students at least 25 times, prosecutors said Friday in federal court in Boston. He was paid a total of $240,000, they said.

A Harvard graduate, Mark Riddell had an uncanny knack for standardized tests, able to calibrate his answers perfectly to get any score.

Riddell, a 36-year-old former tennis pro from Palmetto, Fla., pleaded guilty Friday to two federal felony charges in connection with the nationwide college admissions scandal.


He faces a sentence of 33 to 41 months in prison under sentencing guidelines, and is the latest defendant to plead guilty in the college admissions cheating scheme that helped the children of celebrities and wealthy power brokers get into elite colleges that otherwise may not have accepted them.

Many of the students were unaware of the fraud. But in at least one case, the daughter of a Silicon Valley hedge fund leader was there when Riddell helped her with the SAT, and gloated about it afterward, prosecutors say.

“They celebrated the successful cheating on the car ride to Riddell’s hotel,” Assistant US Attorney Eric S. Rosen told a federal judge Friday.

After his arrest, Riddell was placed on leave from his job as director of college entrance exam preparation at IMG Academy, a private prep school in Florida that coaches elite high school athletes.

Dressed in a navy blue suit and wearing a black scarf, Riddell appeared calm as he sat in US District Court and told Judge Nathaniel M. Gorton that he understood the charges.

“I’m here to plead guilty to fraud for cheating on the SAT and ACT test,” he told the judge.


Riddell admitted to conspiracy to commit mail fraud and honest services fraud, and to conspiracy to money laundering. He was paid $10,000 for each fraudulent test, prosecutors said.

He is slated to be sentenced July 18. His attorney, Benjamin Stechschulte of Florida, said he would not comment on the case.

The scheme was carried out in two ways: Riddell and others would help students cheat on tests, or fix their scores, with the test proctors allegedly having knowledge of the fraud; or, those involved in the scheme would bribe athletic coaches to list potential students as recruits, which could facilitate their admission, even if the student had never played the sport competitively before, and wouldn’t for the college.

The alleged architect, William “Rick” Singer, 58, of California, who authorities say collected $25 million, has already pleaded guilty and is slated to be sentenced on June 19.

Singer is cooperating with investigators and helped unravel the conspiracy. Authorities say he set up a set up fake charitable organizations that collected bribes from wealthy parents, and funneled the money to coaches and others, such as Riddell, who helped falsify test scores.

Earlier this week, 13 parents, including Hollywood actress Felicity Huffman, said they plan to plead guilty to a sole count of conspiracy to commit mail fraud and honest services mail fraud.

Separately, 16 other parents, including actress Lori Loughlin and her husband, Mossimo Giannulli, were indicted this week on money laundering charges.

The parents allegedly paid bribes ranging from $50,000 to $1.2 million.


Prosecutors have said Riddell knew the material in tests well enough, without any advance information, to help students score well, but not so well that the scheme would raise suspicion.

“Just a really smart guy,” US Attorney Andrew Lelling told reporters in March.

He first helped fix a student’s scores in 2011, Rosen said. He traveled to Vancouver, Canada, where he used fake identification and posed as the older son of David Sidoo, a Canadian businessman, to take the son’s SAT test. The son was admitted to Chapman University in California. Another son was admitted to the University of California Berkeley, allegedly with Singer’s help.

Sidoo allegedly paid Singer $300,000. He has pleaded not guilty and is awaiting trial.

The student who allegedly celebrated the cheating with Riddell was the daughter of Elizabeth and Manuel Henriquez, who allegedly paid $450,000 to Singer, for helping to fix the scores for two daughters, and for bribing a Georgetown tennis coach. The couple has been charged with mail fraud and money laundering.

Federal authorities have also charged several people involved in the scheme, including two people who oversaw the SAT and ACT tests in Texas and California, with racketeering.

After Riddell’s arrest last month, he released a statement through his attorney apologizing “for the damage I have done and grief I have caused . . . as a result of my needless actions.”

“I understand how my actions contributed to a loss of trust in the college admissions process,” he said.


“I will always regret the choices I made,” he added. “But I also believe that the more than 1,000 students I legitimately counseled, inspired, and helped reach their goals in my career will paint a more complete picture of the person I truly am.”

Milton Valencia can be reached at Milton.Valencia@globe.com. Follow him on Twitter @MiltonValencia