Coursework.info, which claims to have more than 120,000 essays and documents, allows teenagers free access in return for contributing some of their work. Those who do not want to contribute are charged pound;4.99 a month.
The website has announced that it has added its entire collection to a database run by TurnitinUK, which helps schools and exam boards fight plagiarism. A spokeswoman for TurnitinUK said students who plagiarised work from coursework.info could now be detected.
Chris Newson, owner of coursework.info, said he wanted to promote good academic practice. "The vast majority of people use our site properly," he said.
Mr Newson said the aim of the site was to allow students to read five or six examples of coursework but to complete their own work themselves. He hoped his company's move would spur the Government to create a code of conduct for the "essay industry".
A spokeswoman for exam board Edexcel, which uses TurnitinUK, said: "Our focus will remain on educating teachers to encourage their students to avoid plagiarism."