Perhaps because it is more often associated with jazz, or because so much of our teaching has traditionally been (and still is) associated with an accurate representation of a score and the idea of right and wrong, improvisation can be a rather intimidating idea for many teachers. It is, however, simply the musical equivalent of being able to express yourself in words without reading a book.
Improvisation does not have to be tonal, it does not have to follow rules and it does not have to have a specific length. Free improvisation for young (and old) pupils is liberating if it has no tonal centre, and why should it? Pupils will often gravitate towards this though, with the learning that takes place as a result. Encouraging pupils to experiment, extemporise, explore ideas is as vital as asking a young child to write their own stories or converse with a friend. It should be a part of their everyday musical life and it is crucial to give them positive reinforcement that it is a good thing as well as offer them a chance to show you ideas they have discovered. Parents often need to be informed of the value of improvisation and should be encouraged to let their child simply play on their instrument with no score or educational parameters. By doing so pupils will start to teach themselves, discover new ideas, sounds, techniques and take ownership of them and the instrument. Some of what they invent and learn will be far more advanced and complex than any amount of conventional teaching via a score will be able to achieve.
Consider how you might incorporate a small amount of improvisation into your lessons this week. Let us know how it went in the forums.