Overview:  In this launch the teacher performs a review of proportions and properties of proportions.  One student offers the idea that a proportion is two fractions put together with an equal sign, and the teacher illustrates this with the example that 1/2 = 4/8.  The teacher also shows students the notation 1:2 = 4:8.  Then, the teacher begins to illustrate properties of proportions using the variables a, b, c, and d.  The teacher shows students that the product of the extremes is equal to the product of the means, and then students suggest other properties of proportions.  The teacher uses the example 1/2 = 3/6 to test the properties that students suggest.  At the end of the review, the teacher has written 5 different properties of proportions on the board.  The teacher gives students an opportunity to ask questions, to which no one responds, and then the teacher tells students to get to work in their groups.

Prior knowledge:  The teacher reviews students’ prior knowledge of the school mathematics concept of proportions.  It seems that students have studied proportions previously, either in this class or another, and the teacher asks students to name the different ways that proportions can be rearranged and still hold true.  Students offer various ideas, although in some cases (e.g., Keith and Paige) it is not clear whether students remember or understand the properties of proportions or whether they are guessing at ways they could rearrange the four variables in the equality.  The review also requires students to use their prior knowledge from school mathematics to manipulate and simplify fractions.

Other points of interest:  The teacher employs an IRF (Wells, 1993) pattern of interaction with students to elicit their ideas and then give feedback to their responses.  The teacher uses the example of 1/2 = 3/6 to give feedback to the different equalities students suggest by testing those equalities with a concrete example.  At the end of the launch, the teacher does not tell students how they will need to use proportions to work on the problem, or which of the properties of proportions they will need to use.  It is possible that the teacher does not want to give away the solution to the problem by giving students too much information.