When I was hired a year ago, I was given a stack of dreadful-looking professional development books during orientation. This was one of those books. Upon further inspection, it didn't look so bad. As it turns out, it was pretty good! It wasn't earth shattering for me, mostly because I was already familiar with many of the strategies from reading copious amounts of professional development books. That said, I did highlight a lot of parts that I want to come back to and try in my classroom.
The book starts off with research that shows that the greatest factor in predicting student achievement is teacher quality. Actually measuring teacher quality is essentially impossible (hear that, reformers and politicians?), but Wiliam has taken some of the guesswork out of the equation by compiling a handful of strategies that have been proven to have the largest impact on student learning, all centered around formative assessment.
What I liked best was Wiliam's writing style. He doesn't talk down to teachers or pretend that he knows what's best. He knows teaching is incredibly difficult, and his book is simply the research behind the most powerful, proven methods in education and some strategies for teachers to try as we see fit.
The idea I found most interesting was centered around feedback. I'm definitely going to work on being more purposeful on how I give feedback and grades, and how I have my students use and interact with that feedback. There were studies which found that if students can work with teacher feedback to achieve a product of higher-quality, learning will improve more than if comments are written and students do nothing with them. Also, giving grades along with feedback, when we want students to USE the feedback, absolutely negates the feedback; students won't use it. So, bottom line: don't grade formative assessments but do give feedback and ensure students act on that feedback in class.
I would recommend this book in particular to teachers who were trained in the era before learning targets and formative assessments were commonplace. These ideas were drilled into my brain in my teacher education program, so a lot of the big ideas in this book were just reminders of what I already knew (but could improve upon still), but I see how older generations of teachers could be impacted heavily and positively.