Students are told to write a "Guess what!" sentence.
Make sure the children know the sentences can be anything and should be surprising sentences.
There are 5 examples in the slideshow to help students see that silly is fine and possibly give.
Included is a powerpoint and worksheet. The worksheet can be printed and then cut into 3 to save paper.
When we did this activity, we gave students 10 minutes to write and said to aim to write 3 sentences so the slower students have at least 1 sentence while the faster students still have something to work on.
After this, have the students say their sentences in pairs and react to each others sentences with phrases like "Really?", "Me too", "That's nice", "That's great", etc.
The students seemed to really enjoy being creative with their sentences.
This activity was made for 1st grade Junior High school New Crown - Take Action! Talk 1, but it can be used for other ages and curriculums.