I have long been impressed by free materials available from the National Academies. They make their materials available free for online reading. Now they are providing free downloads of their materials in PDF format.
My interest in math education led me to the following free book:
Cross, C.T., Woods, T.A., & Schweingruber, H., eds. (2009). Mathematics Learning in Early Childhood: Paths Toward Excellence and Equity. Committee on Early Childhood Mathematics. National Research Council. Retrieved 6/9/2011 from http://www.nap.edu/catalog.php?record_id=12519.
Quoting from this 398-page book:
Early childhood education has risen to the top of the national policy agenda with recognition that ensuring educational success and attainment must begin in the earliest years of schooling. There is now a substantial body of research to guide efforts to support young children’s learning. Over the past 15 years, great strides have been made in supporting young children’s literacy. This report summarizes the now substantial literature on learning and teaching mathematics for young children in hopes of catalyzing a similar effort in mathematics.
The need for this study was recognized and championed by the National Research Council’s (NRC’s) Mathematical Sciences Education Board following the publication in 2001 of Adding It Up: Helping Children Learn Mathematics. The tireless efforts of board member Sharon Griffin and then board director David Mandel led the design of this project, which is a comprehensive examination of the evidence base that can guide mathematics education (teaching and learning) for children ages 2 through 6. It represents the further extension of a portfolio of NRC reports focused on mathematics learning and teaching that includes Adding It Up: Helping Children Learn Mathematics (2001); Eager to Learn: Educating Our Preschoolers (2001); How Students Learn: Mathematics in the Classroom (2005); and On Evaluating Curricular Effectiveness: Judging the Quality of K-12 Mathematics Evaluations (2004).
The National Academies—National Academy of Sciences, National Academy of Engineering, Institute of Medicine, and National Research Council—are committed to distributing their reports to as wide an audience as possible. Since 1994 we have offered “Read for Free” options for almost all our titles. In addition, we have been offering free downloads of most of our titles to everyone and of all titles to readers in the developing world. We are now going one step further. Effective June 2, 2011, PDFs of reports that are currently for sale on the National Academies Press (NAP) Website and PDFs associated with future reports will be offered free of charge to all Web visitors.