Hi Campaspe:
My DD1 was queen of the monosyllabic sentence and we were also set the target of 'work on expanding sentences'.
Our tricks were these:
In the car play 'add a word':
So you might start with integrad's setnence:
The cat watched the mouse patiently
Then your DC could add a word:
Maybe: The HUNGRY cat watched the mouse patiently
Then you could add:
The hungry AND CUNNING cat, watched the mouse patiently.
and so on....
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We also used books DD1 liked against her.
So with the Harry Potter series - we had her write a sentence about Harry. I said write the dullest sentence you can think of ...
DD1 came up with: Harry Potter is a boy.
Then I said now try using that sentence but make it more interesting.
Eventually we got:
Harry Potters seems to be an ordinary boy, but actually he's a wizard.
(We didn't get there in one step:
Step 1: Harry Potter is a boy and a wizard.
Step 2: Harry Potter is an ordinary boy, but he's a wizard.
Step 3: Harry Potter seems to be an ordinary boy, but actually he's a wizard.)
And do the same with Hermione, Hagrid, etc...
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Try the one day an alien came to lunch or class game.
Give them some words like: Monday, lunch, mash potatoes and see what they come up with using the alien came to lunch or class theme.
We also had good success with My Teacher is actually a....
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Once DD1 was used to saying a bit more than just I go to school. I read books. I work hard. type sentences we then followed advice of English Teacher (Senior School level) friend of ours who suggested that DD1 should work on adding 5 senses to her writing:
So when writing a few sentences about a subject try including something about:
SMELL (WHAT IT SMELLED LIKE)
SIGHT (WHAT IT LOOKED LIKE)
SOUND (WHAT YOU HEARD/ WHAT IT SOUNDED LIKE)
TOUCH (WHAT IT FELT LIKE)
TASTE (WHAT IT TASTED LIKE/ OR DID IT LEAVE A BAD TASTE)
Thinking through your senses and using that to help colour what your writing does seem to really help.
HTH