Great science activities don't just happen; they are orchestrated by highly skilled teachers who are creative, caring, and innovative. Effective classroom teachers possess a deep understanding of the developmental characteristics of their students and are adept at translating this understanding into opportunities for individual students to demonstrate their understanding. An effective teacher creates a student-centered learning experience that explicitly links essential concepts and skills to student's current understanding and natural curiosity about the topic. High-quality teachers provide opportunities for students to make choices, to be creative, and to practice and enhance critical-thinking skills, all while holding student interest. Another critical component of high-energy learning environments are creative assessments that stretch student thinking. This article illustrates how the careful structuring of learning experiences within a unit can lead to authentic, student-centered assessment. While the examples provided in this article are from a fifth-grade science lesson, the ideas are applicable to all disciplines and grade levels. Techniques for rich, authentic asssessment are revealed through a polymer gel spheres project. The process followed in developing and carrying out the authentic assessment task featured in this article is not restricted to the chemistry unit described here. This process can be used at other grade levels and within other disciplines.