This activity is good for reviewing grammar such as "I must", "I will" and "I should". You need to be reviewing at least two such grammar points to use this activity.
Have examples of the sentences on the board. Maybe also have a 'fill-in-the-blanks' style template. Depending on the level, you can use cards to prompt what the students should say.
Students get into small groups and decide who will start first. That student starts with one sentence. For example, I will do my homework now. The next student takes that sentence and converts it into the other grammar structure and then adds a sentence of their own. For example;
- Student A:
- I will do my homework now
- Student B:
- If I must do my homework now,
- then I will have a bath tomorrow.
- Student C:
- If I must have a bath tomorrow,
- then I will go to bed late tonight.
You can scale this activity up so that you use more grammar points. You can also link all the sentences together with and. So the first student has one sentence to say, the next two, the third three and so on until someone makes a mistake. Then it starts again.