Today, as more and more people enroll to higher education, educational authorities, and institutions continually need to update their curricula and to find alternative and innovative ways to support the active participation of learners. Student Response Systems (SRSs) have become one of the most common tools used in today's classrooms. Along with the development of technology, several online tools were provided to a sample of teachers in order to conduct an assessment within the classroom environment as an alternative to classic SRSs. "Kahoot!" is one such tool used within the educational setting. The purpose of this study was to reveal the effects of using Kahoot! on preservice teachers' academic achievement, as well as on their retention when Kahoot! was used as a formative assessment tool. This quasi-experimental study was conducted with 91 preservice teachers during the fall semester of the 2019-2020 academic year. Data were collected via three quizzes, a midterm exam, and a retention test. The study's results indicate that the students who were applied paper-based quizzes had higher exam and retention test scores.