Look at NCTM's recommendations for content in the algebra strand in the Standards, then look at the problem for designing square swimming pools. After reading the problem, work on Problems B1-B5.
Read the commentary on the swimming pool problem in "Experiences with Patterning," by Joan Ferrini-Mundy, Glenda Lappan, and Elizabeth Phillips, in Teaching Children Mathematics (February 1997), p. 282-288.