The event is being promoted by long-serving foe of Peabody the Missourians Organizing for Reform and Empowerment, a group that has staged many protests against the coal giants in the past.
The sit-in of around 100 people began on Tuesday and has thus far been a peaceful protest.
Students gave speeches on the grand staircase on Wednesday. They said they wanted Peabody to stop sponsoring the university’s consortium for clean coal utilisation.
Students also want to see Peabody CEO Greg Boyce leave the university’s board of trustees.
In a statement, a Peabody spokesman said the company was “proud to support Washington University in St. Louis and its leadership in education, as well as in clean coal research.”
The last time students at the university picked up their placards was in 2005 which lead to major reforms in compensation for the school’s janitorial staff.
Organiser Molly Gott and MORE are debating their next move, which could include picketing at the Peabody Opera House, at Peabody’s downtown headquarters, or at the Botanical Gardens.
However, the student’s co-operation with MORE has been criticised in St. Louis media, which highlighted MORE’s seeming vendetta against Peabody.
The gathering targeted Peabody despite the university’s ties to other companies in the fossil fuel industry.
Boyce is not the only coal executive on the board of trustees. Arch Coal’s chairman, Steven Leer, also sits on the board.
Peabody, along with Arch Coal and Ameren Missouri helped launch the university’s clean coal consortium in 2008 that focusses on finding ways to minimise coal’s environmental impact.
The three companies committed to a combined $12 million in funding for the institute.
A Washington University spokesman said the university welcomes student expression about coal or any other issues.
“We want our students to be motivated and engaged citizens and to develop into strong leaders,” she said.
“This is a very important part of their academic experience at Washington University.”