Learning by teaching
In the field of pedagogy, learning by teaching (German: Lernen durch Lehren, short LdL) is a method of teaching in which students are made to learn material and prepare lessons to teach it to the other students. There is a strong emphasis on acquisition of life skills along with the subject matter. This method was originally defined by Jean-Pol Martin in the 1980s.
The method of having students teach other students has been present since antiquity. Most often this was due to lack of resources. For example, the Monitorial System was an education method that became popular on a global scale during the early 19th century. It was developed in parallel by Scotsman Andrew Bell who had worked in Madras and Joseph Lancaster who worked in London; each attempted to educate masses of poor children with scant resources by having older children teach younger children what they had already learned.
Systematic research into intentionally improving education, by having students learn by teaching began in the middle of the 20th century.
In the early 1980s, Jean-Pol Martin systematically developed the concept of having students teach other in the context of learning French as a foreign language, and he gave it a theoretical background in numerous publications. The method was originally resisted, as the German educational system generally emphasized discipline and rote learning. However the method became widely used in Germany in secondary education, and in the 1990s it was further formalized and began to be used in universities as well. By 2008 Martin had retired, and although he remained active Joachim Grzega took the lead in developing and promulgating LdL.
After preparation by the teacher, students become responsible for their own learning and teaching. The new material is divided into small units and student groups of not more than three people are formed.
Students are then encouraged to experiment to find ways to teach the material to the others. Along with ensuring that students learn the material, another goal of the method, is to teach students life skills like respect for other people, planning, problem solving, taking chances in public, and communication skills. The teacher remains actively involved, stepping in to further explain or provide support if the teaching-students falter or the learning-students do not seem to understand the material.
Plastic Platypus Learning
One way of learning by teaching, is the plastic platypus learning or platypus learning technique. This technique is based on evidence that show that teaching an inanimate object improves understanding and knowledge retention of a subject.  The advantage of this technique is that that the learner does not need the presence of another person in order to teach the subject.
The name 'plastic platypus learning' is a paraphrase on the known software engineering technique rubber duck debugging, in which a programmer can find bugs in their code without the help of others, simply by explaining what the code does, line by line, to an inanimate object - namely, a rubber duck.
To increase the effectiveness of plastic platypus learning, learners are advised to do the following:
1. Prepare notes while learning the subject.
2. Prepare the lesson on the subject (as opposed to just teaching it unprepared; this section demands the most time and energy, and may be omitted in some situations).
3. Teach the subject without using the notes at all (the student knows this beforehand). 
Obviously, this technique may work with any inanimate object, and not just plastic platypuses.
- Active learning
- Jigsaw (teaching technique)
- Learning theory (education)
- The Aha! effect
- Think aloud protocol
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