Teachers hold your tongues. What you say in a Chinese classroom may or may not be held against you.

Xu Zhuanqing (许传青), an assistant professor at the Beijing University of Civil Engineering and Architecture, learned this lesson the hard way back in April. She was alleged to have made, during a class on probability theory, unspecified remarks suggesting Chinese people were inferior to Japanese. A notice from the university dated April 4 said Xu had been disciplined as a result of her “inappropriate comparisons,” which were “reported by a student after class.”

In early June, Xu Zhuanqing’s case became a focus of interest on WeChat and Weibo, in part due to the popularity of a post on Weibo by user “LiuHu9plus” (刘虎9plus), who introduced a concept to the discussion around the disciplining of Professor Xu that was unfamiliar to many, and an open secret to many others — the use of “student informants,” or xuesheng xinxiyuan (学生信息员), to keep tabs on China’s classrooms.

In a May 30 post, LiuHu9plus wrote: “A professor at Zhejiang University says he originally thought ‘student informants’ only carried out surveillance of teachers in the humanities and social sciences. But after seeing this disciplinary decision [against Xu], they realized that teachers in science and engineering were treated in the same way.”

The topic of “student informants” was cracked wide open. Who were these classroom spies? How and under what conditions were they deployed? By whom? How long had this been going on?

As interest rose, the spotlight turned to other cases. Also in April, Zhai Jiehong (翟桔红), an assistant professor at Wuhan’s Zhongnan University of Economics and Law, was stripped of her teaching responsibilities after she was accused of criticizing recent amendments to China’s Constitution.

In a story about Xu and Zhai with a suggestive headline about “Cultural Revolution winds returning” (文革风重来), Hong Kong’s Sing Pao Daily News quoted a university professor in Shanghai as saying the problem of students informing on their teachers was worsening. “At university students inform against their teachers,” the professor said. “In the future, out in society, who will they inform against?”

The sentiment was echoed in a WeChat private group, where one user remarked, referring to the former East German secret police: “We are all Stasi” (人人都是斯塔西).

Discussants on social media then started digging, and exposed the various “informant systems” (信息员制度) in place at universities. In fact, they realized, universities in China had organized teams of student informants as early as 2008. Ferreted out by one user, a document from the Hunan University of Commerce showed that this was characterized as “intelligence work” (情报信息工作) that was “secretive in nature” (具有隐秘性). It was also paid work. Generally, student informants would receive between 20 and 50 yuan for providing a single piece of information, and for information regarded as more critical they could be paid 200 yuan.

Informant systems were in place not just at universities, however. Others contributing to the discussion found evidence — most of it right out in the open — that the same systems were being implemented in middle schools and even in primary schools. And beyond the education system, there were even “stability maintenance informants” (维稳信息员) being cultivated and deployed in rural townships.

These systems, which in the beginning had been treated as highly secret programs, had in recent years become increasingly open, and it was possible even to find academic papers online that studied these systems. Take, for example, this 2012 paper published in Vocational and Technical Education Forum, a journal openly circulated by Jiangxi Science and Technology Normal University. Written by Yan Guirong (闫贵荣), a scholar from the Tianjin Vocational Institute, the paper is rather explicitly titled: “A Study of the Building and Operation of Student Informant Systems in Professional Schools: Drawing on an Exploration of Practices at the Tianjin Vocational Institute.”

This paper, accessed through the CNKI database of Chinese periodicals, a leading resource for academic studies in Chinese, was shared and discussed in June as attention turned to the issue of “informant systems” and “student informants,” or xuesheng xinxiyuan (学生信息员), a term that appears in the paper. Search the CNKI database now, however, and you find that the paper is missing. In its place is a notice that reads: “The paper you are looking for does not exist.”