The aim of the study is to assess the extent to which WhatsApp Instant Messaging is used to teach chemistry and biology to the tenth-grade students. A mixed approach was used, whereby the authors drew on the content analysis model to analyze quantitative data. The sample consisted of 28 Palestinian tenth-grade students and their teachers, who used WhatsApp Instant Messaging for four months (the Spring semester of 2019). The collected data was divided into four categories: the nature of the message (instructional, organizational, or social); the form of the message (texts, pictures/graphs, voice recordings, videos, or link-sharing); the direction of communication flow (from a teacher to a student, from a student to a teacher, from a student to a student, or from a teacher to a teacher); and knowledge exchange. Our findings suggest that WhatsApp is used more for non-instructional purposes--particularly socialization--yet the portion of instruction-related messages was somehow enough to predict more effective future use of the application for teaching/learning purposes.