It uses the visualising strategy by encouraging students to quickly sketch (not draw in detail) the main points of the text.
I have seen it used with narrative texts, where the students have sketched key points in the story creating something similar to a story board or a story flow chart, but my favourite way to use sketch to stretch is with informative texts.
It is especially good with procedures.
Here is how I have used it in the past:
I will read the text to the students, and they just listen.
I will read it again to the students and this time I will pause briefly at the end of each important part I wish them to sketch (so for instance if it was a procedure I would stop at the end of each instruction). I remind students that it is only a quick sketch - that no one will be judging them on their drawing ability - and that it is simply to help remember the key points.
Then I will read it back to them for a third time, allowing them to write key words (labelling) their sketch and to check that they drew a sketch for each step.
Following the sketching period, I will ask them to reproduce the text in their own words using the sketch as their guide for what to write. Their sketches, if they have done them properly and not skipped sketching a step, should provide all of the information they need to write their procedure in their own words.
I have found this strategy very useful with reluctant and struggling writers who need some assistance to complete writing tasks. This activity, the sketching and key words in particular, provides that much needed framework for those writers.