In 2008, Supreme Court Justice Clarence Thomas decided to send his teenage grandnephew to Hidden Lake Academy, a private boarding school in the foothills of northern Georgia. The boy, Mark Martin, was far from home. For the previous decade, he had lived with the justice and his wife in the suburbs of Washington, D.C. Thomas had taken legal custody of Martin when he was 6 years old and had recently told an interviewer he was “raising him as a son.”

Tuition at the boarding school ran more than $6,000 a month. But Thomas did not cover the bill. A bank statement for the school from July 2009, buried in unrelated court filings, shows the source of Martin’s tuition payment for that month: the company of billionaire real estate magnate Harlan Crow.

The payments extended beyond that month, according to Christopher Grimwood, a former administrator at the school. Crow paid Martin’s tuition the entire time he was a student there, which was about a year, Grimwood told ProPublica.

“Harlan picked up the tab,” said Grimwood, who got to know Crow and the Thomases and had access to school financial information through his work as an administrator.

Before and after his time at Hidden Lake, Martin attended a second boarding school, Randolph-Macon Academy in Virginia. “Harlan said he was paying for the tuition at Randolph-Macon Academy as well,” Grimwood said, recalling a conversation he had with Crow during a visit to the billionaire’s Adirondacks estate.

ProPublica interviewed Martin, his former classmates and former staff at both schools. The exact total Crow paid for Martin’s education over the years remains unclear. If he paid for all four years at the two schools, the price tag could have exceeded $150,000, according to public records of tuition rates at the schools.

Thomas did not report the tuition payments from Crow on his annual financial disclosures. Several years earlier, Thomas disclosed a gift of $5,000 for Martin’s education from another friend. It is not clear why he reported that payment but not Crow’s.

The tuition payments add to the picture of how the Republican megadonor has helped fund the lives of Thomas and his family.

“You can’t be having secret financial arrangements,” said Mark W. Bennett, a retired federal judge appointed by President Bill Clinton. Bennett said he was friendly with Thomas and declined to comment for the record about the specifics of Thomas’ actions. But he said that when he was on the bench, he wouldn’t let his lawyer friends buy him lunch.

Thomas did not respond to questions. In response to previous ProPublica reporting on gifts of luxury travel, he said that the Crows “are among our dearest friends” and that he understood he didn’t have to disclose the trips.

ProPublica sent Crow a detailed list of questions and his office responded with a statement that did not dispute the facts presented in this story.

“Harlan Crow has long been passionate about the importance of quality education and giving back to those less fortunate, especially at-risk youth,” the statement said. “It’s disappointing that those with partisan political interests would try to turn helping at-risk youth with tuition assistance into something nefarious or political.” The statement added that Crow and his wife have “supported many young Americans” at a “variety of schools, including his alma mater.” Crow went to Randolph-Macon Academy.

Crow did not address a question about how much he paid in total for Martin’s tuition. Asked if Thomas had requested the support for either school, Crow’s office responded, “No.”

Last month, ProPublica reported that Thomas accepted luxury travel from Crow virtually every year for decades, including international superyacht cruises and private jet flights around the world. Crow also paid money to Thomas and his relatives in an undisclosed real estate deal, ProPublica found. After he purchased the house where Thomas’ mother lives, Crow poured tens of thousands of dollars into improving the property. And roughly 15 years ago, Crow donated much of the budget of a political group founded by Thomas’ wife, which paid her a $120,000 salary.

“This is way outside the norm. This is way in excess of anything I’ve seen,” said Richard Painter, former chief White House ethics lawyer for President George W. Bush, referring to the cascade of gifts over the years.

Painter said that when he was at the White House, an official who’d taken what Thomas had would have been fired: “This amount of undisclosed gifts? You’d want to get them out of the government.”

A federal law passed after Watergate requires justices and other officials to publicly report most gifts. Ethics law experts told ProPublica they believed Thomas was required by law to disclose the tuition payments because they appear to be a gift to him.

Justices also must report many gifts to their spouses and dependent children. The law’s definition of dependent child is narrow, however, and likely would not apply to Martin since Thomas was his legal guardian, not his parent. The best case for not disclosing Crow’s tuition payments would be to argue the gifts were to Martin, not Thomas, experts said.

But that argument was far-fetched, experts said, because minor children rarely pay their own tuition. Typically, the legal guardian is responsible for the child’s education.

“The most reasonable interpretation of the statute is that this was a gift to Thomas and thus had to be reported. It’s common sense,” said Kathleen Clark, an ethics law expert at Washington University in St. Louis. “It’s all to the financial benefit of Clarence Thomas.”

Martin, now in his 30s, told ProPublica he was not aware that Crow paid his tuition. But he defended Thomas and Crow, saying he believed there was no ulterior motive behind the real estate magnate’s largesse over the decades. “I think his intentions behind everything is just a friend and just a good person,” Martin said.

Crow has long been an influential figure in pro-business conservative politics. He has given millions to efforts to move the law and the judiciary to the right and serves on the boards of think tanks that publish scholarship advancing conservative legal theories.

Crow has denied trying to influence the justice but has said he extended hospitality to him just as he has to other dear friends. From the start, their relationship has intertwined expensive gifts and conservative politics. In a recent interview with The Dallas Morning News, Crow recounted how he first met Thomas. In 1996, the justice was scheduled to give a speech in Dallas for an anti-regulation think tank. Crow offered to fly him there on his private jet. “During that flight, we found out we were kind of simpatico,” the billionaire said.

The following year, the Thomases began to discuss taking custody of Martin. His father, Thomas’ nephew, had been imprisoned in connection with a drug case. Thomas has written that Martin’s situation held deep resonance for him because his own father was absent and his grandparents had taken him in “under very similar circumstances.”

Thomas had an adult son from a previous marriage, but he and wife, Ginni, didn’t have children of their own. They pitched Martin’s parents on taking the boy in.

“Thomas explained that the boy would have the best of everything — his own room, a private school education, lots of extracurricular activities,” journalists Kevin Merida and Michael Fletcher reported in their biography of Thomas.

Thomas gained legal custody of Martin and became his legal guardian around January 1998, according to court records.

Martin, who had been living in Georgia with his mother and siblings, moved to Virginia, where he lived with the justice from the ages of 6 to 19, he said.

Living with the Thomases came with an unusual perk: lavish travel with Crow and his family. Martin told ProPublica that he and Thomas vacationed with the Crows “at least once a year” throughout his childhood.

That included visits to Camp Topridge, Crow’s private resort in the Adirondacks, and two cruises on Crow’s superyacht, Martin said. On a trip in the Caribbean, Martin recalled riding jet skis off the side of the billionaire’s yacht.

Roughly 20 years ago, Martin, Thomas and the Crows went on a cruise on the yacht in Russia and the Baltics, according to Martin and two other people familiar with the trip. The group toured St. Petersburg in a rented helicopter and visited the Yusupov Palace, the site of Rasputin’s murder, said one of the people. They were joined by Chris DeMuth, then the president of the conservative think tank the American Enterprise Institute. (Thomas’ trips with Crow to the Baltics and the Caribbean have not previously been reported.)

Thomas reconfigured his life to balance the demands of raising a child with serving on the high court. He began going to the Supreme Court before 6 a.m. so he could leave in time to pick Martin up after class and help him with his homework. By 2001, the justice had moved Martin to private school out of frustration with the Fairfax County public school system’s lax schedule, The American Lawyer magazine reported.

For high school, Thomas sent Martin to Randolph-Macon Academy, a military boarding school 75 miles west of Washington, D.C., where he was in the class of 2010. The school, which sits on a 135-acre campus in the Shenandoah Valley, charged between $25,000 to $30,000 a year. Martin played football and basketball, and the justice sometimes visited for games.

Randolph-Macon was also Crow’s alma mater. Thomas and Crow visited the campus in April 2007 for the dedication of an imposing bronze sculpture of the Air Force Honor Guard, according to the school magazine. Crow donated the piece to Randolph-Macon, where it is a short walk from Crow Hall, a classroom building named after the Dallas billionaire’s family.

Martin sometimes chafed at the strictures of military school, according to people at Randolph-Macon at the time, and he spent his junior year at Hidden Lake Academy, a therapeutic boarding school in Georgia. Hidden Lake boasted one teacher for every 10 students and activities ranging from horseback riding to canoeing. Those services came at an added cost. At the time, a year of tuition was roughly $73,000, plus fees.

The July 2009 bank statement from Hidden Lake was filed in a bankruptcy case for the school, which later went under. The document shows that Crow Holdings LLC wired $6,200 to the school that month, the exact cost of the month’s tuition. The wire is marked “Mark Martin” in the ledger.

Crow’s office said in its statement that Crow’s funding of students’ tuition has “always been paid solely from personal funds, sometimes held at and paid through the family business.”

Grimwood, the administrator at Hidden Lake, told ProPublica that Crow wired the school money once a month to pay Martin’s tuition fees. Grimwood had multiple roles on the campus, including overseeing an affiliated wilderness program. He said he was speaking about the payments because he felt the public should know about outside financial support for Supreme Court justices. Martin returned to Randolph-Macon his senior year.

Thomas has long been one of the less wealthy members of the Supreme Court. Still, when Martin was in high school, he and Ginni Thomas had income that put them comfortably in the top echelon of Americans.

In 2006 for example, the Thomases brought in more than $500,000 in income. The following year, they made more than $850,000 from Clarence Thomas’ salary from the court, Ginni Thomas’ pay from the Heritage Foundation and book payments for the justice’s memoir.

It appears that at some point in Martin’s childhood, Thomas was paying for private school himself. Martin told ProPublica that Thomas sold his Corvette — “his most prized car” — to pay for a year of tuition, although he didn’t remember when that occurred.

In 2002, a friend of Thomas’ from the RV community who owned a Florida pest control company, Earl Dixon, offered Thomas $5,000 to help defray the costs of Martin’s education. Thomas’ disclosure of that earlier gift, several experts said, could be viewed as evidence that the justice himself understood he was required to report tuition aid from friends.

“At first, Thomas was worried about the propriety of the donation,” Thomas biographers Merida and Fletcher recounted. “He agreed to accept it if the contribution was deposited directly into a special trust for Mark.” In his annual filing, Thomas reported the money as an “education gift to Mark Martin.”