Watching a debate can help people understand multiple points of view. At the conclusion of a debate, a consensus might occur after a deep analysis and discussion of the issues. Most students will participate in a class debate at some point in their schooling, but chances are that debate will not take place in math class. What could there be to debate in a subject that is based on mathematical proof? This article suggests using a debate format in math class to promote the use of critical thinking, academic language, and numerous Common Core Standards for Mathematical Practice (SMP) (CCSSI 2010). By debating classifications within various mathematical domains, students can use definitions and other resources to make arguments that represent their current understanding of a definition and then debate with classmates about opposing opinions. This use of academic language in a rigorous manner will allow students to build a deeper understanding of the interconnectedness of the content. The four-corner debate is an activity in which students move around the room as their ideas on classifications of elements change in response to their classmates' arguments. Four signs are posted, one in each corner of the room, and students use definitions and their own understanding to argue about the appropriate classification of an object, expression, and so forth. This article presents one example of a four-corner debate aimed at grades 6 and 7. The debate focuses on classifying comparison quantities; the possibilities are a ratio, a rate, a unit rate, or none of the above.