The scam, said prosecutors, arranged for children to be recruited as athletes, regardless of their athletic abilities.
"These parents are a catalogue of wealth and privilege", United States attorney Andrew Lelling said at a news conference.
Prosecutors said it was up to the universities to decide what to do with students admitted through cheating.
"I was essentially buying or bribing the coaches for a spot", Singer said as he pleaded guilty to charges including racketeering, money laundering and obstruction of justice.
The Hoover Tower rises above Stanford University in this aerial photo in Standford, California, U.S., January 13, 2017.
Athletic coaches from Yale, Stanford, the University of Southern California, Wake Forest and Georgetown, among others, are implicated, as well as parents and exam administrators, the release says.
Huffman looked distraught as she waited for her hearing at the Los Angeles Federal Court of Justice on Tuesday. Loughlin's husband, the designer Mossimo Giannulli, was also arrested, along with 30 other parents, nine college coaches, two SAT/ACT administrators, an exam proctor and a college administrator.
The fraud scheme was run out of a small college preparation company in Newport Beach, California, that relied on bribes to sports coaches, phoney test takers and even doctored photos to land college slots, USA prosecutors said on Tuesday.
Messages seeking comment from Huffman's representative were not immediately returned.
The man whom authorities allege is at the center of the scheme, William Rick Singer, appeared in a Boston federal courthouse Tuesday. The former Desperate Housewives star looked extremely exhausted as she walked by a number of paparazzi waiting to take her picture.
Huffman and Loughlin are among those charged with conspiracy to commit mail fraud and honest services mail fraud.
Read on for some of the most eyebrow-raising events surrounding the case that have captured people's attention.
In one YouTube post, she talked about the difficulty of juggling her career with school, and said she didn't know how much she would actually attend. A former Yale soccer coach pleaded guilty before the documents went public and helped build the case against others.
In total, 46 people have been indicted in the multimillion-dollar scheme.
The coach, Rudolph Meredith, resigned in November after 24 years running the women's soccer team. Singer pleaded guilty and his lawyer, Donald Heller, said his client intends to cooperate fully with prosecutors and is "remorseful and contrite and wants to move on with his life". Authorities claim parents would pay him a predetermined amount, with full knowledge of what they were doing. The couple allegedly agreed to the plan.
It was not an accident that no students were charged on Tuesday, said Lelling, the U.S. attorney. None of the children were charged on Tuesday.
Another form of Singer's scheme involved paying off officials who administered the SATs, according to the criminal complaint.
The afternoon court appearance is after seven federal officers reportedly showed up at their Hollywood Hills home this morning with guns drawn while the family was asleep, including their two daughters, sources shared with TMZ.