Representing repeating nonterminating decimals as rational numbers is a topic introduced in the seventh-grade Common Core State Standards for Mathematics. According to Content Standard 7.NS.2.D., students should be able to represent a rational number as a decimal and understand that the decimal will either end in zeros or eventually repeat (NGO Center and CCSSO 2010). The lesson described in this article extends this standard by asking students to recognize repeating nonterminating decimals as rational numbers. The lesson focused on a repeating nonterminating decimal that seems to distress students more than most: 0.9 . The lesson was given to three freshman algebra 1- enriched classes at a large urban high school. Approximately 25 students were in each class, and classes were 48 minutes long. The goal of this lesson was to reveal student thinking about 0.9 and 1 by investigating the value of these numbers through number lines, comparisons, arithmetic operations, and algebraic manipulations.