KWL:Lesson

What strategy would you use to asses student's prior knowledge and why?

I would use the K-W-L three column theory. The K stands for what students know, or think they know, before they begin to read. The W stands for what students want to know or think they will learn. The L stands for what the students have learned (after reading). This approach is a great tool for assessing prior knowledge and as a refection strategy after the reading as occurred.
Because writing is reading and reading is writing, this tool is very effective!