Student or Learner
"If necessary, the parties will draw up a plan, in writing, detailing the materials to be used."
I think "in writing" is superfluous because "draw up" implies it. What say you?
In legal or quasi-legal texts, you need to say exactly what you mean- you could draw up a plan orally, or even on a whiteboard, etc, but it needs to be formalised in writing to be recognised as such.