Most students can’t tell the difference between real news articles and sponsored content, according to a study from Stanford University, raising concerns over how young people consume online media. As The Wall Street Journal reports, the study is the largest to date on how young people evaluate online media, involving 7,804 students from middle school to college. It will be published on Tuesday.

According to the study, 82 percent of students could not distinguish between a sponsored post and an actual news article on the same website. Nearly 70 percent of middle schoolers thought they had no reason to distrust a sponsored finance article written by the CEO of a bank, and many students evaluate the trustworthiness of tweets based on their level of detail and the size of attached photos, according to the Journal.

The US presidential election has sparked a debate over how Facebook and other web companies treat fake news articles, which some have blamed for spreading misinformation ahead of the vote. Facebook CEO Mark Zuckerberg has said the company is working on systems to limit the spread of false information, and Google will ban fake news sites from its lucrative ad network.

But the Stanford study suggests that students still struggle to evaluate the credibility of online sources, making it difficult to sift through more subtle forms of misinformation such as advertising and sponsored posts. Schools have begun offering more media literacy courses, the Journal reports, but they also have fewer librarians to help teach basic research skills. Stanford professor and lead author Sam Wineburg tells the Journal that students should learn to cross-check the legitimacy of websites using other sources, and to not always equate a site’s high Google search rankings with accuracy.