Our overarching goal in reading is comprehension at deep levels of understanding. There are many tools that help to achieve this. One of these tools is writing.
When asking students to write about reading, you should have them write in an authentic way (that's for them, not for you!) This can look very different for all students.
Writing long is just one way of fleshing out thoughts about your reading. However, if you see that kids are writing beautiful essay-like writing about their reading every day, and it's totaling about the same amount of time (or more) as their actual reading, they are probably not using their time wisely.
Writing about reading can be short, messy, and organic. It can be on a post-it, index cards, or in a notebook. It can be in phrases, sketches, or short sentences. They can create timelines, tables, T-charts, or anything. You should teach your student different ways to organize their thoughts, always highlighting how these help comprehension. This will enable kids to create their own ways to write about reading.
One final tip is that when kids write about their reading, you should ask them to think about how this will influence their next round of reading. If it doesn't, then it really didn't help them!
What role does writing play in your teaching of reading? How does it enhance your students' comprehension? What questions do you have about this important topic?