This is a technique I learned on a training course for 1:1 tutors, and it is designed to support pupils who find it difficult to come up with ideas and to structure their writing. An example in its most basic form would be using the nursery rhyme Jack and Jill.
This boxes up into the simple story:
This could become:
This second story follows exactly the format of the first, but with enough details changed to make it a new story.
The source text can be carefully chosen to help with whatever the pupils are struggling with – eg a descriptive piece to help them use more adjectives, or to understand how to include similes and metaphors within a piece of writing.
This technique can be used as closely or loosely as needed to support the child, beginning by boxing up every few words, moving onto every sentence and finally every paragraph until the pupil is confident enough to structure a piece of writing unaided.