Teaching materials like textbooks or work sheets can be opened up to free redistribution and the option to change it for everyone. What are the arguments for doing this, with respect to how it can benefit the quality of education? Are there examples or is there evidence of it having the effect?
Sure it can but...
It would not necessarily be better than regular materials. School boards often spend money getting customized programs / information. This may not always happen if all the information is open sourced.
Some examples of this:
The catholic school board in Toronto has used companies to get custom software for its students: