Giving writing a purpose

The more I work with my ALL writing intervention group, the more I am noticing just how important giving writing a purpose is.  While creating a book wasn't planned at the beginning, it is now going to be the final product of their first piece. 
Right back at the beginning, our first lesson started off as a brainstorm of ideas and interests.  Over the past 4 weeks, that brainstorm has turned into amazing descriptive writing that is full of adventure and suspense.  As the students writing progressed we decided that because it was so good we needed to publish it, so have decided on a book. 
During independent writing, the students are all publishing their own work (another step which has great benefits).  When I was reading one students work aloud yesterday I came across a couple of sentences that didn't sound right.  The student was quick to say "Yeah I came across those errors when I was publishing Mrs O'Callaghan, and I made the changes on the computer".  I was stoked to hear this.  In the past, because the students didn't have an audience for their writing, other than me, their attempts to proof-read and edit were minimal.  Now because they are publishing their work as a book, the quality of their proof-reading and editing has improved ten fold.
The use of descriptive language has been a major focus for us.  Trying to hook our readers and then sustain their audience throughout the ENTIRE piece has required a lot of talking and sharing of words and ideas.  However, I am so pleased to say all the group are now using amazing words throughout their piece.  After reading a students work aloud to a fellow teacher this morning, I heard my top writer say to his friends "I am going to start doing stink writing so I can get into the ALL group".  Still not sure if this is a good thing of not :)
Yesterday for our release session, the group were told that since they are all authors who are creating their own book, they needed to come up with a gripping title which would capture attention if it was in a library amongst thousands of books, yet not give away the adventure and suspense in the story.  They also they needed to begin illustrating the cover, again without giving away too much information, whilst still giving the potential reader enough information so that they could determine whether it would be of interest to them.  Again, I can't express enough, just how powerful sharing ideas aloud as a group is.  The first book titles that the group thought of included: The war story; My adventure story; My OMG adventure.  As the ideas began to flow, so to did their ideas.  In the end we came up with a page of possible gripping titles such as: What a weird day!; Did that just happen?; Am I dreaming?; What did this book do to me?; My near death experience!; You will never believe what happened to me today!.
The entire group are so excited about creating a proper book.  This morning I knew I was heading down the right track when three of my most reluctant writers came up to me before school and asked if they could carry on working on their books.  Of course I was thrilled to hear this.  These boys are high energy boys that love to be outside playing and running around, but because they are having so much fun creating a book, and can see themselves as authors, they preferred to be inside continuing with their masterpiece. 
While my long term goal was for all of my students to develop a love of writing, to see themselves as writers, and to be confident at writing, I truly believed it would take much longer than 4 weeks.  I am blown away to see such an amazing transformation in attitude towards writing, at such an early part of the intervention.
My initial inquiry question was about removing the barriers that struggling writers face and help them overcome these while writing.  The way the intervention is going at the moment, I feel I am half way there.  My next big challenge is to now continue what has been happening, with more of a focus now on transferring their learning to their independent work.  I also aim to address a lot more of the surface features.