Audio-visual aids are effective teaching tools because learners retain 20% of what they hear, 30% of what they see, 50% of what they see and hear, 80% of what they say, and 90% of what they say and do. According to Edgar Dale's Cone of Experience, using real objects and hands-on experiences is the most effective way for students to learn, followed by using simulations, field visits, and audio-visual aids. Some common audio-visual aids include charts, pictures, models, flashcards, slides, projectors, maps, boards, computers, TVs, and virtual classrooms.