For the CBM writing assessments, they get a writing prompt, which they complete with a brief story or personal narrative. It is not copying, but original writing. ("One day I was walking on the beach, when I found a bottle. There was something in it. When I opened the bottle...").

This pdf explains how to administer and score a 4-minute writing assessment:

http://www.jimwrightonline.com/pdfdocs/cbmresources/cbmdirections/cbmwrit.pdf

This page has a few comments about writing probes, and a form for making prompts, including some clickable pre-made prompts (in the sidebar):

http://www.interventioncentral.org/teacher-resources/curriculum-based-measurement-probes-writing

The writing assessments on the PAL-II include both copying (sentence and paragraph) and composition. If you're going for a strong school assessment, this would be best, but if you think you're going to have to document on your own, then collect the CBM probe data.

...pronounced like the long vowel and first letter of the alphabet...