This research was conducted to suggest a set of WhatsApp activities to enhance pedagogical knowledge and classroom practices that can be used in TEFL courses and to explore student-teachers' reflection towards the use of WhatsApp and the suggested activities. By reviewing related literature of using social networks and WhatsApp and though interviewing (9) TEFL instructors and (17) TEFL student-teachers, the researcher was able to suggest several activities that were used effectively in TEFL courses. These activities are: (1) reading materials (2) prediction ideas to get interest for the next lecture (3) videos (4) questions for flip classes or reviewing questions or proposing a problem to solve (5) open discussion topics or reflection on the lecture. A set of bases for using WhatsApp activities such as: posting clear content and having clear instructions for doing the activity, meeting FL student-teachers' language level or little higher language level, and not overloading TEFL student-teachers was presented. A group of (104) TEFL student-teachers from the faculty of education at Al-Azhar University-Gaza completed the following three reflection questions: what are the benefits of using WhatsApp and the suggested activities? What are the disadvantages of using WhatsApp and the suggested activities? What are the recommendations for improving the usage of WhatsApp applications and the suggested activities? Their responses were analysed qualitatively and quantitatively. The most common benefits were classified under (a.) pedagogical knowledge (b.) classroom practices (c.) review and evaluation (quizzes or tests) (d.) course requirements. On the other hand, the mentioned disadvantages were classified as (a.) technical and security problems (b.) communication problems.