Understanding and doing science are fairly traditional features of a 21st-century science curriculum. Talking and acting on science, however, are often overlooked and underused, and exemplify the 21st-century emphasis on using knowledge to meet a purposeful goal. We have found that, together, the four ways of knowing are a helpful guide for planning learning goals, selecting materials, shaping activities, and structuring assessments. The following sections describe each area of knowing in greater detail.