A classic activity which can be used to target a wide range of grammar structures, vocabulary, etc.

Students are told that they need to write four sentences, three are true and one is false.  The teacher can specify what the sentences must be about, for example: “write four sentences about yourself using the present perfect” or “write four sentences about San Francisco that use the vocabulary words we learned yesterday.”

Once all of the students have written their sentences, put them into small groups to exchange their sentences.  After a student reads his/her sentences, the other students must guess which one is not true.  Once all of the students have read to their group, the students who managed to stump their group can read their sentences to the class.