Below are a number of multiple choice questions to try to help those with autism and language and speech development delays understand idioms more easily in context. This approach I would find easier compared to having to write continuous prose.  

After having a go at these questions, one is welcome to try and think up, and write sentences of their own for each idiom in question.

1. “Look, it’s raining cats and dogs,” said character A. “If it continues raining like this, there could be flooding issues.”
How much rain is likely to be raining?
A. Lots of rain
B. Not much rain
C. No rain

2. “You’ve done a great job on the garden,” said character B. “The homeowner will be over the moon.”
How will the homeowner feel about the job done on the garden?
A. Very pleased
B. Satisfied
C. Angry

3. “That exam was like a piece of cake,” said Character C to his friend. “No wonder many of our classmates scored a high mark.”
How must the class have found the exam?
A. Easy
B. Average
C. Difficult

4. “It’s getting late, and I’m tired after all the day’s activities,” said Character D to his housemates. “Time for me to hit the hay.”
Where do you think Character D is planning on going?
A. Out somewhere
B. Getting something to eat or drink
C. Bed

5. “If we don’t tidy our mess, she’ll go bananas,” said Character E.
What does character E think the reaction of someone is going to be if the mess isn’t tidied?
A. Pleased
B. Satisfied
C. Angry

6. They went the extra mile to ensure the party was, and went according to the family’s wishes and satisfaction.
How much work must have been done to ensure the success of the party?
A. Lots of work
B. An Average amount of work
C. Not much

7. “Well done,” said the teacher to one pupil. “You’ve hit the nail on the head.”
Is the pupil likely to have got an answer to a question
A. Right?
B. Nearly right?
C. Wrong?

8. I’d quite fancy the idea of owning a big house with a swimming pool, big garden, cinema, and perhaps a gym. The only problem is that a house like that would likely cost an arm and a leg.
Would the house, being talked about, likely be expensive or cheap?

9. The team started playing better towards the end of the game. However, the horse had long since bolted.
What would have been the team’s likely outcome at the end of the game?
A. Win
B. Draw(Scores equal)
C. Loss

10. We’ll be cooking up a storm this Christmas, as we’ll be having plenty of guests for Christmas dinner.
How much food would you say you’d need to cook in order to have enough for lots of guests?
A. Lots of food
B. An average amount of food
C. A very little amount of food

There is also a link to one of my blog post here. It is based on using short stories to try and help those with autism understand idioms more easily.