Teachers provide materials, media and general direction as needed but the children take the ideas where they want. The inquiry and investigation is directed by the children. The teachers observes what happens when the children come in contact with the deliberately chosen materials.
The teacher then provides additional materials and media to expand students' ideas and theories, that allows students' continue to test their theories for accuracy and to reflect upon their learning. The image of the child is one of competency, interested in exploration, creative and motivated to engage.
This is an excellent way to observe what children already know about a range of science topics or to watch what they can create and how they use math manipulatives.
(also allows children to play with and explore manipulatives prior them begin introduced during math instruction)