|12 Months Ended|
Dec. 31, 2020
|Net Revenues Disclosure [Abstract]|
The components of net revenues for the years ended December 31, 2018, 2019 and 2020, are as follows:
K-12 education assessment and other services revenues primarily include K-12 education assessment services and content development services.
Deferred revenue is recorded when the Group has an obligation to transfer goods or services to a customer for which the Group has received consideration from the customer. Part of the balances as of January 1, 2018 and 2019 were recognized as revenues during the years ended December 31, 2018 and 2019. In addition, changes in the deferred revenue balances during the year ended December 31, 2019 included RMB163,400,000 of deferred revenue acquired in connection with the Huanqiuyimeng Acquisition. See Note 3.
Changes in the deferred revenue balances during the year ended December 31, 2020 are as follows: