Most often, students do not write an entire story using all of the steps of the writing process in one 45 minute session. They may complete a draft but rarely is it expected that students who are learning to write also complete the revision process in the same amount of time. Matter of fact, rarely does anyone do that. Therefore, in order for students to be successful when they do the real thing on the writing assessment, they need to try it out and get a sense of what it feels like to do all of that thinking and work at once.
Students are given the prompt and the directions are read through with a emphasis on the sections of the directions that they should review and refer to in order to meet all of the prompts expectations. I remind students to break up their time in a way that gives them enough time to complete each step although each student might need more or less time then their peer to complete certain steps. However, I ask them which step do they think will require the most time? They say drafting and revising. For 4th grade students in my class, drafting - actually writing, is the most time consuming. They don't nearly spend as much time on revising, especially during an assessment, that I hope they did.
Once we've reviewed the strategies, prompt, and direction, I set the timer, a visual timer clock that they can use to keep them focused an on track, I ask them to start writing.
After the 45 minutes is up, we discuss as a class how we thought the process went. Students get an opportunity to share how they felt while doing it. Most felt anxious but some were excited about the prompt because they thought it was interesting and had a great idea to write about. We also talked about the amount of time they used for each section and if they needed more or less time for any particular section. They also share anything else about the assessment and ask questions.
If student's haven't finished, they may either use free time in class to finish it or take it up. In reality, they will have at least two hours to complete the assessment writing and could have longer. I don't expect students to spend more than one hour on completing it after the 45 minutes they had during this lesson. Therefore, any work the do beyond the lesson would still be supporting their ability to complete the task during the real assessment.