This is a pre-assessment strategy.  The teacher will have a pre-determined set of statements that relate to the unit topic. Students that agree with the statement stand up, those that disagree sit down. The teacher then chooses a student who is standing to explain their rationale. If no student is standing then also ask students that are sitting down about their rationale. The teacher can compile a mental observation anecdotal of what the students know and don’t know, or jot down notes/names of what level the students are at. This activity will provide the baseline of students knowledge in relation to the topic and at the same time encourages all students to be active participants.