The document describes a discovery learning model used by a teacher to teach 9th standard students about irrational numbers. The teacher presents examples of numbers and has students observe and group them. In the first stage, students group the numbers as variables or non-variables. In the second stage, they group them as rational, irrational, or variables. Through this activity, students develop an understanding that irrational numbers are numbers that cannot be written as a ratio of two integers, like 1/2 or √2. The teacher then has students practice identifying irrational numbers in different examples.