The Differentiated Classroom - Carol Ann Tomlinson

(...)  So many students ara physically present and psychologically absent. About 40 percent of students go through the motions, neither trying hard nor pay- ing attention. So many cut class and are truant, so many admit to cheating to get through, so many lose interest because they cannot keep up, and so many are bored by the lack of appropriate challenge. So many do not learn that ability is not enough and effort is crucial. About half of students who drop out say their classes were not interesting, and about two-thirds say not one teacher cared about their success in learning at school. Not all is rosy with teachers, teaching, and school. 

http://www.ascd.org/ASCD/pdf/siteASCD/publications/books/differentiated-classroom2nd-sample-chapters.pdf