The Framework for K-12 Science Education, the foundation for the Next Generation Science Standards, identifies scientific explanation as one of the eight practices "essential for learning science." In order to design professional development to help teachers implement these new standards, we need to assess students' current skill level in explanation construction, characterize current teacher practice surrounding it, and identify best practices for supporting students in explanation construction. This multiple-case study investigated teacher practice in eight high school science inquiry units in the Portland metro area and the scientific explanations the students produced in their work samples. T

eacher Instructional Portfolios (TIPs) were analyzed with a TIP rubric based on best practices in teaching science inquiry and a qualitative coding scheme. Written scientific explanations were analyzed with an explanation rubric and qualitative codes. Relationships between instructional practices and explanation quality were examined.

The study found that students struggle to produce high quality explanations. They have the most difficulty including adequate reasoning with science content. Also, teachers need to be familiar with the components of explanation and use a variety of pedagogical techniques to support students' explanation construction. Finally, the topic of the science inquiry activity should be strongly connected to the content in the unit, and students need a firm grasp of the scientific theory or model on which their research questions are based to adequately explain their inquiry results.