Social network sites (SNSs) provide users many mechanisms to share personal information and to restrict access to disclosure. In this regard, users’ privacy-protective and -precarious practices often occur simultaneously. However, past research on SNS privacy issues has often focused on one side of these privacy practices. Additionally, underage students (aged 9–17) constitute a population of SNS users that is less investigated. Many ineligible students (aged less than 13) are in the habit of using Facebook. Their reckless online behaviors sometimes land them in trouble. To investigate underage students’ privacy-protective and -precarious practices simultaneously, cross-sectional surveys were given to students in the primary, middle and high schools around Taiwan. We employed cluster analysis and discovered four clusters as a result. The relationships between memberships and demographical variables as well as other variables such as parental mediation or Internet use were explored as a validation of the clustering results. It was found that membership was related to age, gender, network size and parental mediation. Different interventions are suggested based on these profiles.