Ideally, we would like our students to deeply absorb what they learn in school, but let's be honest, students will probably forget much of the content they learn regardless of our methodology. The same is true for adults; if we don't use it, we lose it. Retention of content is definitely not the main goal of my class, but retention is important for connecting ideas and applying knowledge.
Teachers need to design activities that allow students to explore, discover, and create. This type of learning promotes retention and intrigue--a far more important goal. Bloom's revised taxonomy (2001) listed "create" as the highest level of learning and understanding. At the very least, we should allow our students to design a project format or develop the essential questions.
This type of learning can never be accomplished using inauthentic worksheets and textbooks. At best, this promotes brief memorization. At worst, it threatens to alienate our students from a genuine interest in learning--a serious danger to education and society. We need to create learning environments that excite students to explore and discover our amazing world and create something authentic and unique. This way they internalize the content, so it means something to them. This is how we create life-long learners; this is an ingredient to a 21st Century education.