Generate a full detail guide for teachers on fostering a 'growth mindset' in the classroom, based on Carol Dweck's research. The guide must be actionable. It should include: 1. A clear explanation of 'fixed' vs. 'growth' mindset. 2. A list of specific verbal phrases to use, such as praising effort over intelligence ('You worked so hard on that!') 3. A guide to framing challenges and mistakes as learning opportunities. 4. An example of a classroom activity designed to teach the concept of a growing brain. Please include a supportive disclaimer.