In our opening Math Department meeting, we all participated in the following activity. First we drew a two-set Venn Diagram, where one circle would contain everyone who was an oldest child in the family and one would contain everyone who was the youngest. We quickly agreed that if you were an only child you would be in the intersection of the sets, and if you were a middle child you would be in the fourth region, outside the two given sets. All was well.
There were several goals to this activity, such as thinking about representation as a “big idea” in algebra and sharing information about ourselves at an opening meeting. In service of the latter goal, we each put ourselves in the appropriate region and described our siblings’ ages and occupations.
But all was not well after all. There were issues. What about half- and step-siblings, for example? Do you straddle the line between two regions? And what about someone who grew up as an only child until he was in college, when his parents adopted his younger sister? (In terms of typical birth-order issues he was an only child for a long time, before becoming the oldest child.) And what about people who just didn’t want to talk about their siblings, or perhaps didn’t even want to acknowledge their existence? Probably all these questions could be discussed amicably and unemotionally in a group of collegial adults, but do these issues rule out using the activity with a group of teenagers? Should math class be a refuge from awkward topics that some kids don’t want to discuss?