CNN  — 

A dozen college coaches, sports administrators and test administrators each pleaded not guilty to racketeering in federal court in Boston on Monday as part of the sprawling college admissions scandal.

Gordon Ernst, Donna Heinel, Laura Janke, Ali Khosroshahin, Mikaela Sanford, Steven Masera, Martin Fox, Igor Dvorskiy, Lisa “Niki” Williams, William Ferguson, Jorge Salcedo and Jovan Vavic each pleaded not guilty to racketeering during their arraignments.

Ernst, Khosroshahin, Janke, Vavic, Salcedo and Ferguson were college coaches. Heinel was the senior associate athletic director at USC. Williams and Dvorskiy were standardized test administrators. Masera and Sanford were employees of Key Worldwide Foundation, the company at the center of the alleged fraud. Fox was the president of a private tennis academy and camp in Houston.

The court hearing comes two weeks after prosecutors announced charges against 50 people accused of carrying out the largest college admissions fraud ever prosecuted in the United States.

Prosecutors said the defendants carried out a scheme to cheat on standardized tests and/or bribe college coaches, who then helped the prospective students gain admission to a university by falsely claiming the students were athletic recruits.

Of the 50 defendants, four people have pleaded guilty or plan to plead guilty in the case, according to prosecutors. Rick Singer, the mastermind of the scheme; Rudy Meredith, the Yale women’s soccer coach who accepted a bribe to help a student get admitted; and Mark Riddell, who cheated for the students on the SATs and ACTs, are all cooperating witnesses for the prosecution. John Vandemoer, the former Stanford head sailing coach, has also pleaded guilty.

A total of 33 wealthy parents were charged with conspiracy to commit mail fraud and honest services mail fraud for their role in the scheme, according to court documents. Many of these defendants are scheduled to appear in federal court in Boston in the coming two weeks. Actresses Lori Loughlin and Felicity Huffman are expected to appear in court on April 3.

Michael Center, the head coach of the men’s tennis team at the University of Texas at Austin, is also charged with conspiracy to commit mail fraud and honest services mail fraud and is scheduled to appear in court on March 28.

Additional arrests are expected as the investigation continues, according to a law enforcement official familiar with the investigation.

These arrests could include students older than 18 and parents. It’s unclear at this time if any more schools or school officials will be implicated.

Investigators are expecting to charge more than five others within four to six weeks, according to the official, who cautioned the investigation is ongoing and this is subject to change.