These lessons reinforce students' understanding that some changes happen quickly and others can take a long time. Lessons 15 and 16 serve as a second embedded assessment. In Lesson 15, selecting substances previously used in the unit or new substances with properties similar to those used earlier, students create their own recipes to bring about a specific change. In Lesson 16, students exchange recipes and demonstrate the changes that occur in each case. This embedded assessment allows students to analyze the changes they have observed during the unit and apply what they have learned earlier.
Additional assessments provide further opportunities for evaluating student progress.