This study develops two scales, namely, the outside school social media behavior (OSSMB) scale and inside school social media behavior (ISSMB) scale, to measure the types of behavior that adolescent students engage in on social media in two separate contexts: outside school and inside school. Data collected from 814 students in four Hong Kong secondary schools were divided into two equal data sets (n = 407 for each) by random selection and then analyzed. Principle component analysis (PCA) and confirmatory factor analysis (CFA) were used to generate and test the structures of the two scales on the different data sets. The PCA results showed good factor loadings for all items (all above 0.60), and satisfactory total variance were explained by the both structures (69.06% for the OSSMB and 75.30% for the ISSMB). The CFA results showed acceptable model fits for both first- and second-order CFA for both scales. The internal consistency for all factors (and subdimensions) and the two scales were also acceptable. The 21-item OSSMB scale has four subdimensions: "Consuming," "Communicating," "Creating," and "Sharing." The 10-item ISSMB scale has three subdimensions: "Consuming," "Creating," and "Sharing." In conclusion, this study provides new tools and conceptual frameworks for assessing students' social media behavior in two contexts (i.e., outside and inside of school).