could be improved. This learning progression suggests ways in which students of different ages could learn age-appropriate versions of core ideas with understanding, rather than addressing them in current haphazard ways. This learning progression also suggests priorities in the curriculum, helping to identify the conceptual tools and practices that are the foundation for critical learning.
Suggesting appropriate ages for introduction of key ideas. For example, many textbooks and state curricula introduce atomic-molecular stories (not functional as models) as early as third or fourth grade, while the national science education standards delay atomic-molecular models until high school. This research suggests why middle school students could benefit from learning to use atomic-molecular models and what the key elements of those models might be.
Large-scale and classroom assessment. This learning progression suggests the most important conceptual tools and practices to be assessed, common alternatives or misconceptions, and specific questions or tasks that could be used (for an extensive discussion of assessment in the learning progressions framework, see Smith et al., 2006).
Classroom instruction. What is known about mechanisms of learning can be useful for guiding classroom instructions: key questions to address with children of different ages, important experiences that may move the process of succession forward, and key conceptual tools and practices that can be introduced and mastered.
Taken together, these literatures (on preschool understanding, mature scientific understanding, the response of children to sustained good instruction) along with societal expectations and values could form a powerful set of constraints on the development of a set of plausible learning progressions. Clearly, though, there could be more than one way to make choices about what core ideas should be the focus for learning progression analysis. Undertaking the intellectual task of thinking through detailed learning progressions for different end-state core ideas, however, might be one step in thinking through possible advantages and disadvantages of different approaches. In addition, even if we agree on focal core ideas that are the target of instruction and a learning progression that connects the two end points, it would not fully prescribe the instructional sequence. In much the same way as there are constraints on how a complex structure such as a house can be built from its starting components—for example, certain things such as the foundation and then walls must come first to provide structural support for the windows and roof—yet within those constraints there is some flexibility as well and multiple ways to build a house.