From the website:
DLESE is the Digital Library for Earth System Education, a free resource that supports teaching and learning about the Earth system. DLESE's development was funded by the National Science Foundation and continues to be built by a distributed community of educators, students, and scientists to support Earth system education at all levels.
DLESE is operated by the National Center for Atmospheric Research (NCAR) Computational and Information Systems Laboratory and the NCAR Library on behalf of the education community.
* Easy access to quality teaching and learning resources about the Earth as a system for a wide range of learners * Services to help users effectively create, use and evaluate digital learning resources * Interfaces and tools to allow student exploration of Earth data
Resources in DLESE include lesson plans, scientific data, visualizations, interactive computer models, and virtual field trips - in short, any web-accessible teaching or learning material. Many of these resources are organized in collections, or groups of related resources that reflect a coherent, focused theme. In many ways, digital collections are analogous to collections in traditional libraries.
All resources in DLESE have been contributed by community members, are relevant to Earth system education, and are checked periodically for technical stability. The Reviewed Collection includes those DLESE resources that have been more closely examined and are considered exemplary.
Finally, DLESE serves as the geoscience node in the National Science Digital Library (NSDL). NSDL serves the broader communities of science, technology, engineering, and math education.