"Learning is not a spectator sport. Students do not learn much just by sitting in class listening to teachers, memorizing repackaged assignments, and spitting out answers. They must talk about what they are learning, write about it, relate it to past experiences, apply it to their daily lives. They must make what they learn part of themselves. (Chickering & Gamson, 1987)

In a typical classroom setting, students are often only passively in learning, i.e., in listening to the instructor, looking at the occasional overhead or slide, and reading (when required) the textbook. Research shows that passive involvement generally leads to a limited retention of knowledge by students, as indicated in the 'cone of learning' developed by Edgar Dale shown below. (McKeachie, W.J., 1998)

"Active Learning" is, in short, anything that students do in a classroom other than merely passively listening to an instructor's lecture. http://www.calstatela.edu/dept/chem/chem2/Active/index.htm

The notion of active learning suggests that students must do more than simply receive information and substantive material but must also engage and participate in activities and tasks that enhance comprehension, understanding, and knowledge. http://pegasus.cc.ucf.edu/~jmorris/asatrg/jaffee.htm

…students must do more than just listen: They must read, write, discuss, or be engaged in solving problems. Most important, to be actively involved, students must engage in such higher-order thinking tasks as analysis, synthesis, and evaluation.
http://www.ntlf.com/html/lib/bib/91-9dig.htm

It involves putting our students in situations, which compel them to read, speak, listen, think deeply, and write. While well delivered lectures are valuable and are not uncommon, sometimes the thinking required while attending a lecture is low level comprehension that goes from the ear to the writing hand and leaves the mind untouched. Active learning puts the responsibility of organizing what is to be learned in the hands of the learners themselves, and ideally lends itself to a more diverse range of learning styles.
http://edweb.sdsu.edu/people/bdodge/active/ActiveLearningk-12.html

…the common goal is the provision of opportunities for learners to integrate new information, concepts, or skills into their own mental schema, through rephrasing, rehearsing, and practice. Activities can utilize group methods such as brainstorming, buzz groups or small group work. Individuals can experience active learning through paper and pencil exercises or individual seat work.
http://www.lib.utexas.edu/is/publications/active.html

Most students have spent the majority of their school career in passive learning environments in which faculty were disseminators of information, and students were required to memorize information or use specified algorithms to solve problems. In an active learning environment, students are encouraged to engage in the process of building and testing their own mental models from information that they are acquiring. In such a learner-centered environment, faculty become facilitators of learning, and students become active participants, engaging in a dialog with their colleagues and with the instructor. http://www.uth.tmc.edu/apstracts/1996/advances/March/7s.html

References:

• Dale, E. (1969). Audio Visual Methods in Teaching, (3rd ed). Holt, Rinehart, and Winston.
• Chickering, A.W. & Gamson, Z.F. (March 1987). Seven Principles for Good Practice. American Association Higher Education Bulletin, 39:3-7.
• http://www.cte.usf.edu/bibs/active_learn/nurse/bib_nurse.html
• McKeachie, W.J. (1998). Teaching tips: Strategies, research and theory for for college and university teachers. Houghton-Mifflin.