Chapter 14 of Critical Thinking About Critical Periods, edited by Donald B. Bailey, Jr., Ph.D., John T. Bruer, Ph.D., Frank J. Symons, Ph.D., & Jeff W. Lichtman, M.D., Ph.D.

Copyright © 2001 by Paul H. Brookes Publishing Co. All rights reserved. No part of this excerpt may be reproduced or reprinted without permission in writing from the publisher.

In preparing this book, we asked each author to present his or her own perspective on critical periods in a defined area of expertise or development. We did not set out necessarily to draw a single conclusion or reach consensus. Rather, we wanted the full range of perspectives as substantiated by existing data. Thus, we have assembled an array of chapters, each of which addresses the concept of critical periods from a different point of view. What have we learned from this?

The first message that will likely be taken from this book is that the concept of critical periods in its purest sense — a defined period of time during which it is essential for normal development that certain experiences occur — probably is not the most appropriate term to describe early human development or to justify policy decisions regarding practices with children. And this is not just a lesson in semantics — reflecting disagreements over whether one term (e. g. , critical period, sensitive period, window of opportunity) is most appropriate. We have too much evidence about the remarkable ability of humans to change and learn from experience at virtually every age to conclude that the early childhood years are necessarily more important than other years. Thus, caution is clearly warranted in the use of this term and the arguments we make to support efforts to improve quality of early care and education for children.

Having said that, however, there is unanimous agreement that human learning begins at least at birth, if not before. From the moment a child enters this world, he or she forms perceptions about the nature of life and relationships with others. Even if we cannot justifiably apply the term critical period to the earliest years, experience is the unquestioned basis by which these perceptions are formed. To use the analogies suggested by several authors in this book, the windows of opportunity begin to open at birth. It logically follows that when a window of opportunity opens, we should take advantage of it, even if we don't have evidence that doing so now is necessarily better than later. We certainly do not have any evidence whatsoever that once a window opens, later is better.

Several future directions for research and practice are clear. First, different windows open at different times. Thus, teachers and parents need to know general developmental milestones so that we know when it is and is not appropriate to focus on specific skills. Although we know a great deal about development already, research is needed to clarify when windows of opportunity generally open for certain specific skills, and this information needs to be made available to parents and teachers in a much more accessible format.

Second, each child follows a unique developmental course. Thus, knowing general developmental milestones does not ensure that we know when to begin to provide certain kinds of experiences for an individual child. Effective parents and teachers are aware of each child's level of development and provide experiences that are challenging enough to promote development but not so challenging that they result in constant failure or frustration. Research is needed on how best to identify individual opportunities for learning, and tools are needed that parents and teachers can use with individual children.

Third, there is no point in trying to teach something if the window is not yet open. For example, a 12-month-old child is not ready to learn letters of the alphabet. Thus, providing these experiences earlier would make little sense and, in fact, could easily be harmful. We need research that helps us understand the potential negative consequences of too much stimulation of the wrong type, and this information needs to be made more accessible for families and teachers.

Finally, it is clear that inequity exists in our society in the extent to which children have opportunities for access to various experiences after certain windows open. For example, when the language window opens (probably at birth), almost all children have access to sufficient sounds and social interactions to develop language. But, some children have access to more complicated language and more supportive language than others. The inequity magnifies when the windows of opportunity for learning to read begin to open. Some children have dramatically more opportunities to be read to and to experience books and printed materials than other children. Research is needed on effective programs that help eliminate such societal inequities, and policies need to be enacted that make such programs a reality.

This book continues to affirm the importance of appropriate experiences during the early childhood years. Indeed, as the first period during which humans have extensive interactions with and feedback from the environment, the early childhood years constitute our first opportunity as parents and as a society to influence development. Although opportunities for influence continue throughout the life span, they begin during early childhood; and, thus, early childhood constitutes a period during which we should pay close attention to what children experience and how these experiences shape later development. The real issue is the vast differences in opportunities for children today to develop needed skills, even though the window of opportunity for this development is quite long. Children living in impoverished and other high-risk environments often miss out on important learning opportunities provided for more advantaged children in today 's society, putting them at risk for substantial delay in development and setting a pattern of educational failure that is difficult to overcome. Thus, while we contend that there is no magical critical period, early intervention for children at risk of school failure remains an important national goal.

The ultimate purpose for thinking critically about critical periods is to improve our understanding of the mechanisms regulating early development. By understanding what we know and do not know about early development from both a brain and behavior perspective, informed and rational interventions designed to alter development can be tested. The goal from an applied practice and policy perspective is to improve the health and welfare of children whose development is at risk for any number of reasons. Among the chapters in this book, none was definitive regarding practice or policy initiatives. We hope that this fact alone will help us all to realize the strength of multiple perspectives working together and aimed at the common goal of understanding the early development of young children and the factors that can interfere with optimal development. It is important to note the italicized "can," because much of what we know from the biological perspective is based on controlled experimental studies with different species, with findings that are suggestive but not necessarily absolute when the human condition is considered. Moreover, studies from the behavioral and social sciences share problems common to sampling limitations, quasiexperimental designs, and correlational data. The point is that the methods used by different domains of inquiry have strengths and weaknesses. Thinking critically about how our knowledge is generated can help us learn more about what we already know, what we do not know, and what we need to know. As research continues and new possibilities for early intervention evolve, the intersections between basic brain science and the behavioral and social sciences will become busy places full of promises and pitfalls. Intervention work will continue to be one of the most visible contexts for exploring the difficult questions raised by basic researchers and seized on by policy makers.

We hope that this book has helped clarify for the field the nature of the arguments surrounding critical periods and has provided a basis for the next generation of research. This research should not focus so much on trying to prove that critical periods do or do not exist, because this will be virtually impossible to determine, but rather on what is the nature of developmental risk in today's society that potentially could be addressed through programs of prevention and education.