This performance assessment pilot study was a major research component of the overall National Science Foundation funded Redesigned High Schools for Transformed STEM Learning Project. Secondary Earth/Environmental Science students' abilities to translate cognitive knowledge into demonstrable performance-based proficiencies were specifically examined. Proficiencies assessed included evaluation, prediction, analysis, synthesis, and reasoning in the contexts of soil and water, clouds and weather, acid rain, and astronomy-based performance tasks. This manuscript presents research protocols, implementation process, and collective determination of proficiency rates among Project student participants. Results of the pilot study indicated that approximately 48 percent of student participants demonstrated performance-based proficiency of knowledge. Implications on evidence-based iterations of school models, state mandated assessment practices, and classroom factors in support of performance-based proficiencies are discussed.