The transfer of matter and energy from one organism to another and between organisms and their physical setting is a fundamental concept in life science. Not surprisingly, this concept is common to the "Benchmarks for Science Literacy" (American Association for the Advancement of Science, [1993]), the "National Science Education Standards" (National Research Council, [1996]), and most state frameworks and likely to appear in any middle-school science curriculum material. Nonetheless, while topics such as photosynthesis and cellular respiration have been taught for many years, research on student learning indicates that students have difficulties learning these ideas. In this study, nine middle-school curriculum materials--both widely used and newly developed--were examined in detail for their support of student learning ideas concerning matter and energy transformations in ecosystems specified in the national standards documents. The analysis procedure used in this study was previously developed and field tested by Project 2061 of the AAAS on a variety of curriculum materials. According to our findings, currently available curriculum materials provide little support for the attainment of the key ideas chosen for this study. In general, these materials do not take into account students' prior knowledge, lack representations to clarify abstract ideas, and are deficient in phenomena that can be explained by the key ideas and hence can make them plausible. This article concludes with a discussion of the implications of this study to curriculum development, teaching, and science education research based on shortcomings in today's curricula.