Decomposers is one of six units in the Carbon: Transformations in Matter and Energy (Carbon TIME) curriculum, which was developed through an NSF-funded research collaboration focused on learning progressions to support environmental literacy. These units were developed for middle and high school students. The units are designed in three groups; each group increases in scale from the previous one. Students should first complete the foundational unit, Systems & Scale (http://carbontime.bscs.org/systems-and-scale), which uses the process of combustion to build basic concepts of matter, energy, and organic compounds at the atomic-molecular scale.The Decomposers unit is one of three units at the organism level, and students are intended to complete one or more of these three units. These units are intended to be followed by one or both units at the systems level. Each organism scale unit focuses on three questions: (1) Where are molecules moving? (2) How are atoms in molecules being rearranged into different molecules? and (3) What is happening to energy? In the Decomposers unit, students investigate fungal growth and decay through the anchoring phenomenon of molding bread. The highly guided sequence of six lessons in the unit guides students to identify patterns from their observations, develop a model for fungal growth and activity, and then apply that model to explain the growth of bread mold and other decomposers. This model includes extracellular digestion, biosynthesis, and cellular respiration. Extensive supporting infomation is provided within each lesson and on the resources page (http://carbontime.bscs.org/resources). The assessment site (http://ibis.colostate.edu/MSP/CTIME/Index.php) includes pre-/post-tests for each unit and for the overall curriculum. The overview provided here (http://media.bscs.org/carbontime/files/unit_synopses.pdf) provides a helpful orientation to this complex resource.