Although interest in preschool science is not new in the United States, this area of learning is enjoying renewed attention among those concerned with prekindergarten education and with improving scientific literacy and achievement among the nation's citizens. Despite the increased interest and funding investment in early science education and the expectation that high-quality educational supports will result in improved school readiness and achievement in science and related domains, research and program evaluation efforts are limited by a lack of appropriate assessments for learning and classroom instructional quality in science. This article reports on a number of promising tools and approaches for evaluating children's learning progress in science and the quality of instructional supports for this learning. The article discusses learning and knowledge assessments, which include supporting and assessing science learning during everyday interactions; performance-based assessments for individualized instruction, progress monitoring, and curricular evaluation; direct assessments of science learning; and assessments of science-relevant skills and dispositions. The article also discusses classroom quality measures related to science learning.