The current study seeks to shed light on the usage habits of the "WhatsApp" application among teenagers, exploring the effect of mobile instant messaging distractions on pupils' working memory performance. Research was conducted in Israel during 2016 school year. The study sample was divided into two groups randomly--a control group and an experimental group. Researchers used six questionnaires to gather personal details, execution assessment questionnaire, and Working Memory Index from the Wechsler Intelligence Scale for Children-IV. The main findings show that "WhatsApp"'s distractions, transmitted via smartphones, decrease pupils' performance of working memory. In addition, students are aware of the difficulty "WhatsApp" causes while performing a learning task and of the decrease in learning effectiveness. The present study displays a unique experiment that explored the direct effect of the distractions stemming from a new technological platform--"WhatsApp"--on young pupils' working memory. Further, it suggests that instructors and teachers should be aware of the potential damage of multitasking caused by smartphone use during learning tasks.