Twists in books

I am a strong believer of utilising twists in books – particularly middle grade.  Let's be clear here what we are talking about – I see a twist as something unexpected, a sudden turn in the story – often in the end.  I feel it encourages, more than a happy ending does, a repeat reading – something crucial at this age.  Also it facilitates readers to look at what they are reading more critically to see if they can pick the twist given the clues in the book – again an important skill.