Target Models are complex mental models that students can effectively use to explain real life situations and models that are scientifically correct although not entirely complete at the expert level. These targeted concepts take into account recommendations from the National Standards in Science. Attention is paid to what basic concepts students would need to master in order to use the final model to explain new situations in their world. Target models are determined based on student developmental readiness, prior experience with the content, and understanding of prerequisite concepts. Therefore Target Models are not necessarily the scientific model but may be a more naïve model that is appropriate for the age of the student and their other content background. On their way to the target model students may construct many intermediate models that show varying stages of (complexity and/or articulation that may be the result of) criticisms and revisions of their initial preconception. In addition, each target model builds on the model made for the previous target, allowing for the integrated model at the end of the unit. In this curriculum unit there are 8 major target concepts that students construct on their way to developing an integrated, complex mental model of respiration. While examining how the students were going to attain these target concepts, researchers uncovered learning pathways that take into account realistic developmental abilities of middle school students.

Often students far surpass the target, coming much closer to the scientist's model. However, the first goal is for all students to attain the basic target models in order to provide a solid base for further study of biology and to aid them in real life application of their knowledge. In order to help students in constructing a dynamic and integrated model of the systems of the human body that are involved in energy transfer, as well as integrating the systems with the cellular activity, eight specific target concepts were developed.

The eight Target Concepts are:

1. The body needs energy for all life processes.
2. Glucose is supplied to all cells through the breakdown of food by the digestive system and diffusion into the circulatory system.
3. The body is made up of cells that are in patterned arrangements in the tissues and organs of the body.
4. The cells of the body share many of the same features, but cells from different parts of the body also have some features that are unique. The structure of cells is related to their function.
5. The mitochondria are organelles in the cell where the energy from food and the oxygen from the air is transformed to ATP, a high-energy molecule, for use in many body processes. This process is called cellular respiration.
6. The circulatory system is a closed system that consists of fluid, tubes and a pump. It functions, in part, as a transport system for moving oxygen and glucose to the cell and removing wastes.
7. Oxygen is supplied to cells of the body through the lungs via the alveoli that allow oxygen to diffuse into the circulatory system for transport to the cells.
8. The heart is a dual pump that connects systemic and pulmonary circulation and allows for efficient movement of gases to and from the cell.