Vol.1, No.1 (February 2026)

 Serial No.001

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A Thought Experiment on Population as an Institutional Design Variable in 21st-Century Japan

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Jian Zhang
East Asian Educational Research Institute (General Incorporated Association)

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Abstract

This paper presents a thought experiment that integrates the concept of "optimal population" with the design principles of school education systems, premised on the long-term population decline in 21st-century Japan. Recognizing that the concept of optimal population in demographic research has shifted from the conventional "single-constraint model" to a "multi-objective equilibrium model," this study examines the paradigm shift required of educational systems under the "passive equilibrium" brought about by population decline. Specifically, it discusses the transition of educational units from age-based cohorts to learning opportunities, the redefinition of the social functions of schools, and the necessity of redesigning the very concept of school scale. Furthermore, by articulating multiple theoretical coordinates—including sustainability discourse originating from the Club of Rome's The Limits to Growth, well-being indicators represented by Sen's capability approach and the OECD Better Life Index, and the conceptualization of education as a public good integrated with Samuelsonian public goods theory—this paper presents an intellectual foundation for redesigning Japan's educational system. The conclusion demonstrates that, considering the strong inertia of population dynamics, current educational policy faces the challenge of actively designing a desirable equilibrium between society and education based on the premise of a smaller future population. This paper aims to provide a new theoretical perspective for research on educational systems in depopulating societies.

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Keywords

optimal population, school education, depopulating society, institutional design, sustainability, education as a public good

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1. Introduction: From the Institutionalization of Population Issues to Institutional Design

In 21st-century Japan, population issues have transcended the scope of short-term policy agendas such as "countermeasures against declining birthrates" and have entered a stage that necessitates a fundamental reconsideration of national institutional design itself. Previous discussions have focused on responding to structural problems such as the pace of population decline, aging rates, and regional disparities. However, recent trends in international demographic research pose a more fundamental question: What is the long-term sustainable total population for Japanese society, given its finite land and resources, existing social infrastructure, and current level of technological development?

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This paper attempts to integrate a thought experiment concerning this "optimal population" with the design principles of school education systems. Education is one of the social systems most structurally constrained by population demographics, yet the impact of changes in total population on the long-term configuration of these systems has not necessarily been sufficiently theorized. While population discussions have concentrated on social security and labor markets, education has consistently been treated as a system operated on the premise of a given population. This paper proposes a perspective that re-envisions population not as an exogenous variable but as an object of active institutional design.

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2. The Transformation of the Optimal Population Concept: From Single Constraint to Multi-Objective Equilibrium

Twentieth-century theories of optimal population were characterized primarily by attempts to estimate upper population limits based on single constraint conditions such as food production capacity or land carrying capacity. Under the premise that population was determined by natural and physical constraints, the primary concern was how much increase was possible.

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However, in contemporary demographic research, optimal population is no longer understood as a single maximum value. While building upon discussions originating from the Club of Rome's The Limits to Growth (1972), it has been reconceptualized as an equilibrium point established among multiple social objectives: environmental impact and sustainability of resource use as core constraints; per capita living standards and subjective well-being—diverse value criteria not captured by mere economic indicators, as demonstrated by Sen's capability approach and the OECD Better Life Index; stability of social security systems; productivity through technological innovation; and even the viability of local communities. In other words, optimal population represents a dynamic optimal range emerging from trade-offs among these elements, rather than being given as a fixed numerical value.

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Viewed from this perspective, the characteristics of Japan's population discourse become clear. In Japan, discussions that would policy-wise set the desirable size of the total population have scarcely been institutionalized. Population decline has been accepted as a given trend, with emphasis placed on institutional adaptation to its consequences. While there exists a certain accumulation of policy measures in areas such as responding to changes in population structure, adjusting regional distribution, and reforming social security systems, the fundamental question of what scale of society should serve as the premise for designing the future has not been explicitly addressed.

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This stance was pragmatic in the sense of avoiding social friction that might result from abrupt population policies. However, at the same time, it cannot be denied that by treating total population itself as a given outcome, choices concerning society's future vision have been effectively deferred to the future. Consequently, Japanese population research has primarily focused on issues of structure and regional distribution, with a strong tendency to treat total population as an exogenous variable resistant to adjustment.

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Yet now that Japan has entered a long-term phase of population decline, this very premise demands reexamination. Rather than treating population size as an exogenous variable, we must reposition as the starting point of institutional design the question: At what scale of society can sustainability, quality of life, and social creativity coexist? Optimal population theory is not a discourse about the abundance or scarcity of population; it is an attempt to question 21st-century design philosophy itself—namely, where to locate society's desirable equilibrium point.

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3. Passive Equilibrium as a Consequence of Population Decline

Japan's population has already entered a declining phase and is projected to converge toward a smaller population size than the present by the latter half of this century (National Institute of Population and Social Security Research, 2023). What is important here is that this future image is not a policy-selected future but a result that follows from current trends in births and deaths.

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"Passive equilibrium," as used here, refers to a state in which society does not actively choose a desirable population size through policy but instead converges toward an equilibrium range consistent with sustainability as a consequence of trends in births, deaths, and migration. In contrast, "active equilibrium" represents an attitude—seen, for example, in Dutch land planning or French national planning—that pursues an optimal combination of population size and social institutions through policy intervention. Japan, in accepting population decline as a trend and concentrating on institutional adaptation to its effects, has clearly followed the path of passive equilibrium.

At the same time, however, this process is not merely one of contraction. Decreased population size potentially approaches an equilibrium range consistent with sustainability in relation to factors such as urban infrastructure maintenance costs, energy consumption, and land use density. In this sense, Japanese society may gradually converge toward a sustainable scale through the long-term process of population decline, rather than through deliberate efforts to design an optimal population.

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This passive equilibrium has decisive implications for educational systems. Education is an institution that prepares society for the future, yet its institutional design is always constrained by the number of children currently existing—that is, by past birth behavior. Educational systems therefore change with a lag of one generation behind demographic fluctuations.

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4. Paradigm Shift in School Systems Under a Depopulating Society

Japan's twentieth-century school system was formed under the implicit premises of population growth and economic expansion. Its three characteristics—homogeneous grouping by age, school placement premised on large-scale institutions, and mass education through standardized curricula—were rational within that historical context.

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However, in a society with a shrinking population, these premises themselves become institutionally difficult to maintain. Issues such as school consolidation and fluctuations in teacher supply and demand are merely surface phenomena. The more fundamental transformation lies in a shift in the organizing principles of educational systems.

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First, the unit of education shifts from age cohorts to learning opportunities. As population declines, maintaining uniform groups of the same age and pace becomes less rational, making institutional designs based on diverse learning pathways increasingly necessary.

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Second is the redefinition of the social functions of schools. In areas with declining population density, schools come to assume roles beyond educational institutions—as mechanisms for sustaining local communities, hubs for lifelong learning, and foundations for social inclusion. This implies strengthening their character as a form of social common capital approximating Samuelsonian public goods. The external effects of education extend beyond individuals and contribute to the sustainability of entire local communities. Consequently, the raison d'être of schools can no longer be justified solely by quantitative indicators such as enrollment numbers.

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Third is the transformation of the logic of educational investment. Quantitative expansion, which was rational during periods of population increase, becomes unsustainable during population decline. In a society with a shrinking working-age population, enhancing each individual's creativity and intellectual productivity becomes crucial for maintaining overall social vitality. Education must therefore be repositioned from a mechanism of selection and efficiency to an investment aimed at maximizing human potential.

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5. Responding to Criticism: Does Smaller Scale Reduce Educational Quality?

A major anticipated criticism of this argument is the claim that population decline makes it difficult to concentrate educational resources and therefore undermines educational quality. From the perspective of economies of scale, the proliferation of small-scale schools might appear to reduce fiscal efficiency and make it more difficult to assign specialized teachers. Furthermore, as population concentration in urban areas progresses, maintaining small schools in depopulated regions may be regarded as inefficient.

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However, such criticism often depends on the assumption that educational quality must be measured according to uniform standards. Research on remote area education demonstrates that small-scale schools possess distinctive educational advantages, including multi-age collaboration and close interpersonal relationships among students and teachers. These characteristics can foster forms of mutual learning that are difficult to realize in large institutions.

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Moreover, developments in information and communication technology make it possible to share educational resources beyond geographical constraints. The apparent isolation of small-scale schools can therefore be mitigated through digital connectivity, enabling diverse forms of learning environments that link local communities with wider educational networks.

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One might further argue that networking educational opportunities would be easier in densely populated urban areas and that implementing ICT-based learning networks in depopulated regions might instead increase costs. However, the networking of educational opportunities is not primarily a function of population density; rather, it depends on institutional design and public investment. Experiences with distance education in countries such as Finland and Canada demonstrate that learning networks in sparsely populated areas can be constructed through policy commitment and the redefinition of teachers' roles. In this sense, the disadvantages associated with small scale can be mitigated through institutional creativity. Downsizing should therefore be reconsidered not as a deficit but as an opportunity for qualitative transformation.

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6. Implications for Educational Research: Redefining the Concept of Optimal Scale

The greatest challenge facing educational systems in a depopulating society is the redefinition of the concept of school scale itself. In Japan, the Ministry of Education, Culture, Sports, Science and Technology's Guidelines on Optimal Scale and Optimal Placement of Public Elementary and Junior High Schools (2015) define the optimal size of schools as approximately 12 to 18 classes. This standard reflects the institutional rationality of the period of population growth, emphasizing both the educational benefits of group interaction and the efficiency of teacher allocation.

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However, with the increasing number of municipalities whose populations are below 30,000, this standard is gradually shifting from a goal to be maintained to a historical condition that requires reconsideration. The issue is not simply maintaining schools by reducing their size. Rather, it involves redesigning educational organizations themselves in ways appropriate to a small-scale society.

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In this context, practices such as combined classes, integrated elementary and junior high schools, compulsory education schools, and regional study-abroad programs should be understood not merely as temporary measures but as early forms of an educational model suited to a small-scale society.

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This discussion also connects with international educational theory. The OECD's Future of Education and Skills 2030 framework presents education as a society-wide learning ecosystem rather than as an activity confined within school buildings. In such a framework, the key issue is not the size of individual schools but the nature of the networks that generate learning opportunities.

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Japan's accumulated research on remote area education also supports this perspective. Postwar studies have examined small-scale schools not only as disadvantaged institutions but also as environments that foster educational potential through multi-age collaboration and close social relationships. In a depopulating society, such knowledge should no longer be treated as pertaining only to marginal cases but rather as anticipating the future conditions of mainstream education.

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7. Conclusion: Population Inertia and the Time Horizon of Education

Population is a variable with strong inertia, and its effects shape social institutions over decades. Educational systems—requiring long-term investments in facilities, teacher training, and curriculum development—are among the institutions most strongly affected by demographic fluctuations.

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Consequently, the object of current educational policy should not be the present population but the already emerging society characterized by a smaller population scale. The key question facing 21st-century Japan is therefore not whether the population can be maintained, but at what population scale a desirable equilibrium between society and education can be achieved.

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Optimal population theory should not be regarded as a peripheral topic within population policy. Rather, it constitutes a fundamental condition for reconsidering the scale of schools, the organization of learning, and the mechanisms through which intellectual reproduction occurs within society. In this sense, the issue of optimal population represents one of the longest time horizons that educational research must confront. This column is intended as a starting point for that discussion.

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​References

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日本へき地教育学会編（2018）『へき地・小規模校教育のフロンティア』.

Meadows, D. H., et al. (1972). The Limits to Growth. Universe Books.

OECD (2011). How's Life?: Measuring Well-being. OECD Publishing.

OECD (2017). The OECD Handbook for Innovative Learning Environments. OECD Publishing.

Samuelson, P. A. (1954). "The Pure Theory of Public Expenditure". The Review of Economics and Statistics, 36(4), 387-389.

Sen, A. (1999). Development as Freedom. Oxford University Press.

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