On the SAMR Model Twine lies somewhere between Redefination and Modification. The tool greatly modifies the writing experience. Adding branching storylines, gamification elements, and RPG elements. The tool would be great for secondary school age students to show their writing skills along side other skills such as: coding, art, and storytelling.
Twine 2 is the newest iteration of the site, utilizing a browser based system which removes the need to download twine.
Twine 2 Visual Representation of the story.
A playlist of 28 videos that goes deeper into the possibilities of Twine and teaches some of the more technical pieces very well.
Twine 2 also has a Wiki that covers a lot of the functionality of the tool. However as of right now I have found some parts of the wiki are still incomplete, so the videos might be a better place to look
Alternatively if you are having problems with the coding portions of the tool, there is a much better Coding Language Manual that covers the ins and outs of the language.
There are many examples of projects made in twine and other similar projects on the Interactive Fiction Database.
One of my favorites from the database is this RPG like story. It has a lot of game elements and basic RPG elements as well.