Education authorities in Xuzhou, Jiangsu province, are investigating a training institution that gives full-time Sinology classes to primary and middle school students who are supposed to be attending regular schools — including the daughter of pop singer Sun Nan.

In 2017, the Ministry of Education issued a notice stressing that local education authorities should pay close attention to students who attend private training institutions full-time in lieu of normal compulsory education.

The authorities should make sure these students return to regular schools, it said.

Xiong Bingqi, deputy director of the 21st Century Education Research Institute, said students attending classes provided by such institutions cannot get a high school diploma, which means they cannot take the national college entrance examination and receive higher education.

"If the institution is found to provide full-time education for primary and middle school students, it should be closed and those in charge should be banned from opening educational institutions again," he said.

The institution, Huaxia College of Traditional Culture, entered the public spotlight when the wife of pop singer Sun said in an interview that the whole family moved from Beijing to Xuzhou three years ago so that Sun's daughter with his ex-wife could attend Sinology classes and learn responsibility and filial piety.

The institution's WeChat account said the classes offered to teenagers cost 96,000 yuan ($14,200) a year and include three years of middle school and another three years of high school.

The classes teach students a wide range of subjects, including traditional Chinese classics, painting, calligraphy, needlework, cooking and flower arrangement.

The content and high price of the classes sparked widespread discussion in social media, and reminded netizens of "female virtue classes" that brainwashed young women and girls into believing that women are inferior and should be obedient to their husband at all times.

Female virtue classes have been popping up in different cities in China. Claiming to promote traditional Chinese values and customs, the classes encourage women to defer to male power and unconditionally obey the orders of their husbands and fathers.

Concepts taught in the class include: "Women should remain in the bottom of the social class" and "The best dowry for a girl is her virginity."

It wasn't clear whether or not the classes Sun's daughter attends are female virtue classes, but the institution itself is registered as an extracurricular training institution, which means it cannot teach primary and middle school students full time.