Two students come to the front of the class. One faces the class (Student A), while the other stands behind him/her and performs an action (Student B). Student A then asks three other students what Student B was doing. Two of the three are allowed to lie. One must tell the truth. Student A must guess which answer is correct.
Assign which students may lie and which may tell the truth by giving each a slip of paper with their role written on it.
For large classes:
After the whole class has seen the activity done once or twice, the teacher may divide the class into small groups. Students in each group will take turns performing each role.
To add a degree of difficulty, additional roles can be assigned. For example, Students B and C perform two different actions at the same time. Answers will follow the structure: Student B was Xing while Student C was Ying. Optionally, one student can only lie about Student B while the other can only lie about Student C.