Because the curriculum follows a learning pathway, the order in which you teach each part of the unit is important. Guidelines have been given in the timelines for longer and shorter versions that still allow students to construct a complex model that is integrated and dynamic. At the same time, however, some flexibility is allowed in whether you choose to teach the whole unit at once or divide it up to teach in two different grade levels. If you do decide to divide up the unit, we recommend teaching the following configurations together:

• Energy - Cells - Cell Structure and Function - Mitochondria
• Or: Energy - Digestion - Pulmonary - Circulation
• Or: Energy - Pulmonary - Cells - Cell Structure and Function - Mitochondria
• Or: Energy - Digestion - Cells - Cell Structure and Function - Mitochondria

Traditionally, the cell is taught in isolation of the systems. We find that this usually leads to students having models that are not integrated or dynamic. Therefore, while it may be necessary to teach the two separately because of school district or State policies, it is important to recognize the connection and to repeatedly reinforce with students the connection. Each chapter has been fit into a certain order so as to create an 'explanatory need'. As students complete one chapter they are left with another question that leads them to ask, "What next". For example, when students have constructed the digestive system and the cell, they realize that they need a transport system to move the glucose to the cell where it is used in making ATP. A carefully placed question at this point helps students realize they need another explanation and this helps to propel the construction process forward toward a complete, dynamic model.

Each Chapter is made up of a number of 'Investigations'. These investigations follow the flow of the critical path. Therefore, unless an investigation or activity is designated as 'Optional', we recommend that you do not skip any. This may interfere with students' construction of an integrated and dynamic mental model of respiration. Most investigations are relatively short, allow ample time for small group work and class discussion. The investigations are written as if talking directly to the student. We found that this allows the teacher the most flexibility in presentation. On one hand, it provides a clear template for how the interaction between the teacher and students might look, providing the teacher with questioning strategies and prompts for students. On the other hand, it provides a detailed lesson that can be given to a student if he is absent. This allows the student to 'catch up' with the group without the teacher or group having to completely redo the lesson. This is important as each lesson builds on the one before and if students miss a class they will need to not only review what was taught but need to actively engage in the lesson in order to construct their own mental model. Sufficient detail is provided that should allow students to engage with the lesson even at home, although working with a partner or small group is preferable.

In addition to the investigation on each page, you will notice that there are several icons that indicate individual, pairs, small group, or whole class configurations. They allow the teacher to quickly know what learning situation is recommended for the particular activity. These symbols are shown below along with what they represent.

• Work together with the small group
• Think and draw individually
• Assess final model
• Share with a partner
• Share with the class

There are also icons that direct you to additional support materials either in the Appendices or on the CD ROM. Chapter endnotes give more information such as scientific explanations and special notes to the teacher to help in teaching a particular lesson. It is highly recommended that you review all such notations before you begin the lesson as they are often very helpful. Pay particular attention to the common misconceptions (alternative conceptions). As you respond to students' models, knowing beforehand the common misconceptions will help you to choose the appropriate activity, discrepant question, or analogy to use in response. It is particularly important to assess often and in an on-going manner. This does not necessarily mean using formal quizzes or tests but can be simply noting each student's model as you more around the room or asking individual students to explain their model. You will find the Assessments in Appendix II. You are free to copy them for your own use. Note that there are numerous quizzes and a test at the end of each Chapter. The following icons are found throughout the investigations.

• Animation
• Transparency
• Misconception
• Assessment

Most lessons follow a pattern we call a GEM cycle (Generate, Evaluate, and Modify). To fully understand GEM cycles and the strategies that support them, please study the video clips on the enclosed CD. In the Generate phase of the cycle the teacher is attempting to encourage students to get out their preconceptions. During this phase students usually are asked to think first individually, then talk to their group and share preconceptions. Finally, students may report out in a whole class discussion. This pattern of individual, small group, and whole class interaction is repeated throughout the lessons. At any point in the Generate phase the teacher is collecting student models and beginning to Evaluate them. This Evaluation is not intended to assess student learning but to determine whether or not the models students hold are compatible with the target. If not, the teacher will use a number of strategies in the lessons to help students criticize and modify their models. The use of these strategies will be easier and better understood if you spend a little time reviewing the video clips on the CD. Feeling comfortable with the strategies will make the lesson more effective and successful for all. Once you apply the strategies be aware that the students may change what they think by modifying initial ideas and even rejecting them. You have to detect the change to determine the effectiveness of the strategy used. If the students went in the expected direction you can proceed to the next section. However, if they have not changed you have to determine what the problem is and then apply a new strategy.