Teaching design patterns in computer science introductory sequence is more difficult than learning it. We present a Just-in-Time-Teaching (JiTT) practice in Software Design Patterns course targeted to entry level students. We proposed a model that combines JiTT concepts with didactic considerations, preparation materials, in-class sessions and post-lecture assignments. We have effectively used this approach to teach two undergraduate classes. The paper also presents the results of a survey conducted to identify the effectiveness of the JiTT activities through warm-up questions, class-wide discussions, experiments and exercises.