serve as de facto mentors for newcomers in hobby groups (e.g., amateur astronomy, gardening).

Productive science learning relationships frequently involve sustained individual inquiry but also intensive social practices with affinity interest groups and in apprenticeship relationships. Distributed and varied expertise in groups allows less knowledgeable individuals to interact with more knowledgeable peers and mentors. Frequently the roles of expert and novice shift back and forth over time, based on specific aspects of the inquiry in question.

Programs, especially during out-of-school time, afford a special opportunity to expand science learning experiences for millions of children. These programs, many of which are based in schools, are increasingly focused on disciplinary content, but by means of informal education. Out-of-school-time programs allow sustained experiences with science and reach a large audience, including a significant population of individuals from nondominant groups. Ensuring that the principles of informal science learning (e.g., learner choice, low-stakes assessments for learners) are sustained as out-of-school-time programs grow will require careful attention to professional development, curricula, and best practices.

One of the more noteworthy features of informal learning settings is the absence of tests, grades, class rankings, and other familiar approaches to documenting achievement that are characteristic of schools. The informal science community has nonetheless recognized the need to assess the impact of informal learning experiences in order to understand how everyday, after-school, museum, and other types of settings contribute to the development of scientific knowledge and capabilities. Everyday interactions about science frequently involve embedded informal evaluation and assessment of activity and reasoning.

In Chapter 3 we outline three criteria that need to be satisfied in order to develop the types of assessments that are most useful for science learn-