Conference Countdown
Atlanta, Ga.
April 2-4, 2016
  • membership
  • my account
  • help

    We are here to help!

    1703 North Beauregard Street
    Alexandria, VA 22311-1714
    Tel: 1-800-933-ASCD (2723)
    Fax: 703-575-5400

    8:00 a.m. to 6:00 p.m. eastern time, Monday through Friday

    Local to the D.C. area: 1-703-578-9600, press 2

    Toll-free from U.S. and Canada: 1-800-933-ASCD (2723), press 2

    All other countries: (International Access Code) + 1-703-578-9600, press 2


  • Log In
  • Forgot Password?


ASCD Annual Conference and Exhibit Show

2016 ASCD Annual Conference and Exhibit Show

Learn. Teach. Lead.
Get the tools to put it all together at this can't-miss education conference—with more than 200 sessions and five inspirational keynote speakers.

Learn more and register.



ASCD respects intellectual property rights and adheres to the laws governing them. Learn more about our permissions policy and submit your request online.

Policies and Requests

Translations Rights

Books in Translation

Premium, Select, and Institutional Plus Member Book (Jan 2003)
Log in to read this chapter.


What Works in Schools

by Robert J. Marzano

Table of Contents

Technical Notes

The following notes are intended to explain some of the more technical aspects of the research findings discussed in this book. These notes, however, are brief treatments of the topics addressed. For more detailed discussion, consult standard statistics textbooks, such as Cohen (1988); Cohen and Cohen (1975); Glass, McGaw, and Smith (1981); Glass, Willson, and Gottman (1975); and Hunter and Schmidt (1990).

Technical Note 1

One of the most common indices found in the research literature is the percent of variance explained (or PV). A basic assumption underlying the use of this index is that the percentage of variance explained by a predictor (or independent) variable (e.g., schooling) relative to a predicted (or dependent) variable (e.g., student achievement) represents the strength of relation between the two. Most commonly, a “set” of predictor variables is used.


You must be an ASCD Select or Premium member to view this content.

Log in.


Log in to submit a comment.

To post a comment, please log in above. (You must be an ASCD EDge community member.) Free registration