There's a great book called Teaching As Leadership which devotes a full chapter to the effect of expectations on a student's performance.

My Kindle reader for Mac won't let me copy and paste, but the following extract from the book is so good that I will type it out:

---------------

While the self-fulfilling prophecy of high expectations is well established by research, in our experience, the most compelling evidence of this idea's power comes from the many testimonials we receive from strong teachers. Crystal Brakke, for example, is a teacher who in her first year teaching eighth grade in Henderson, North Carolina, took her students from almost 70% failing the state literacy assessment to over 80 percent passing it. Ms Brakke shares how her high expectations helped change the academic trajectory of one particularly challenging student.

"The Wilson," the self-appointed nickname of a young man named Scott, was a living legend at Henderson Middle School. He was nearly sixteen years old and had already spent three years at the middle school. The crowds would part in the hallways for him. He ruled the school, and he knew it. He also knew that, probably quite realistically, he would be promoted to high school no matter what he did this school year - we just couldn't keep him in middle school another year. So my second-period class quickly became his personal playground...and I realised that if I didn't do something soon, the year would be lost for both him and the other twenty students I needed to teach...Scott wasn't ready for high school - he was reading at a fifth-grade level.

So I got together with the other teachers on my team, who were facing their own struggles with Scott, and we came up with a plan that was supported by both Scott's grandmother (his guardian) and his older brother, Richard, whom he idolised. We called him into a team meeting, and he sauntered in, ready for whatever we could give him - in-school suspension, after-school detention. He'd seen it all before. Instead, I told him that is schedule had changed: he would now be coming to my class first period and working with the cluster of "gifted and talented" students in that class. Honestly, you could see the color draining from his face. I explained that I realised what the problem was - that it wasn't him; it was me. I wasn't teaching him what he needed; wasn't teaching to his level and expecting from him what I knew he was capable of doing. That's when he just flat out called me "crazy".

But the next day, Scott came to my first-period class. He sat down, and didn't say a word for the next ninety minutes. That's when I knew we were on to something. I can tell you for certain that progress came slowly, very slowly. Some days I had to fight just for him to keep his head up, but then one day, he brought a pen and pencil to class. I almost cried, I was so executed. Another day, he raised his hand to answer a question. He had started participating, and that was the end of behaviour problems with "The Wilson".

By January, he was just another kid in my class and was sharing insights into "Romeo and Juliet" that made my jaw drop. My favourite memory from that year came when one of the seventh-grade teachers approached me after a staff meeting, asking, "What are you doing up there with Scott Wilson?". It turns out "The Wilson" had made a visit to the seventh-grade hallway to chat with some of his old teachers and let them know that we had finally figured it out: he's gifted.