This study introduces a learning environment integrating annotations with a dual-slide PowerPoint presentation for classroom learning. Annotation means a kind of additional information to emphasize the explanations for the learning objects. The use of annotations is to support the cognitive process for PowerPoint presentation in a classroom. The construction of the learning environment is based on cognitive theory of multimedia learning so as to figure out the impact of using annotation in classroom learning. PowerPoint materials and their corresponding multimedia annotations can be simultaneously displayed in the environment. While teaching the current PowerPoint slide, it is displayed through one channel (or projector) and the related annotation or its previous slide is exhibited through the other channel (or the other projector). This manner can scaffold learners' coherent mental representations so as to enhance their learning performance. In this study, an exploratory method was conducted with 170 sophomore and junior students ranging in age between 18 and 21 years. Survey results indicated that the proposed system based on cognitive theory can effectively help students in the experimental group to have better learning efficacy for lectures with dual-slide PowerPoint presentation than that of the conventional group. (Contains 3 tables and 11 figures.)