The value of longitudinal studies during the early years

Author: Centre for Early Childhood
Toddler looking through toy camera

Longitudinal studies — research that tracks large numbers of people over time (see Box 1) — are an essential element of putting data to work for the early years [1].

Tracking children through early childhood and beyond presents three key opportunities for strengthening our understanding of early childhood, providing evidence of:

  1. Why the early years matter: Longitudinal studies allow us to understand the lifelong effects of early childhood experiences and development. 

  2. What matters during the early years: Longitudinal studies allow us to understand the different factors — including educational, emotional, material and genetic — associated with healthy development and the origins of inequalities.

  3. What works in supporting families during the early years: Longitudinal studies allow us to evaluate the longer-term impacts of support provided to families. 

What are longitudinal studies? 

A longitudinal study follows the same people repeatedly over time. 

One form of longitudinal study of particular importance for the early years is birth cohort studies, which follow a group of people born at the same point in time at the very beginning of life and follows them throughout their lives. 

Longitudinal studies can collect a broad range of information about participants’ lives, including information about physical and mental health, social and emotional development, cognitive development and academic achievement, behaviour and attitudes, and employment, income and poverty. 

By collecting information from the same people over time, longitudinal studies provide uniquely rich evidence bases for understanding how people develop and why differences (and inequalities) between people exist. They help us understand how different aspects of our lives interact with each other to affect outcomes. For example, the association between poverty and mental health. 

For further information on longitudinal studies, such as data collection methods and the strengths and weaknesses of longitudinal data, see: https://learning.closer.ac.uk/learning-modules/introduction/

The UK has the largest and longest-running collection of longitudinal studies in the world [2]. These include nationally representative birth cohort studies, including the Millennium Cohort Study, locality-focussed studies, such as Born in Bradford, and longitudinal studies that look at specific aspects of the early years, for example the effects of early childhood education and care (see Figure 1).

Longitudinal studies timeline

These studies have provided a unique window into the importance of the early years, identifying associations between early childhood experiences and development, and outcomes through adulthood. The Dunedin Study, which has followed over 1,000 people since birth for over 50 years, provides perhaps the clearest evidence of the lifelong opportunities presented by promoting healthy development in early childhood [3]. The study also highlights the long-run risks of adverse early experiences, such as socioeconomic disadvantage or maltreatment, which are associated with an elevated risk of mental and physical ill health during adulthood [4]. Evidence from UK birth cohort studies supports these findings, demonstrating the important influence early childhood development has on later outcomes, including educational attainment at the end of secondary school and economic and social outcomes in midlife, such as obesity [5]. 

This evidence of lifelong associations should not be cause for fatalism. We know that associations between early skills and later outcomes decrease in magnitude as people grow older. Most important is learning from the studies about what factors are associated with good outcomes and providing timely support that helps address the challenges families with young children face. 

Longitudinal studies have promoted an increasingly sophisticated understanding of what matters in supporting healthy development in the early years. For example, they have shown us:

  1. Positive early social and emotional development is critical for life-chances: The Dunedin study found that children who had developed strong self-control at age three were more likely to have better health, to be financially secure and less likely to be convicted of a criminal offence—even with childhood IQ and family social class taken into account [6]. Recent analysis in the UK has found a clear correlation between cognitive and socio-emotional development, suggesting a ‘double disadvantage’ for children who have high emotional and behavioural problems [7]. 

  2. Inequalities emerge early: The Millennium Cohort Study shows large gaps in cognitive and socio-emotional development among children at age 3 [8]. Inequalities in development are visible by sex, ethnicity, family socioeconomic circumstances, household structure and maternal mental health. A significant proportion of inequalities in development at age 3 can be traced back to inequalities in the educational, emotional and material environments young children are raised in, explaining over 45% of the inequalities in socio-emotional development [9]. Comparing the Millennium Cohort Study (2000–02) and Study or Early Education and Development (SEED, 2010–12) cohorts, socio-economic inequalities in early cognition and socio-emotional development have not changed significantly [10]. One of the strongest associations between early circumstances and inequalities in development remains family income. Children in the poorest 10% of families rank 31 percentiles lower in cognition and 24 percentiles higher in emotional and behavioural difficulties [11]. While the direct and indirect effects of family income on children’s outcomes are complex, the current context of increasing rates of poverty among families with young children is of concern [12]. 

  3. ‘What parents do is more important than who parents are’ [13]: The Effective Provision of Pre-School Education (EPPE) study found that, for all children, the quality of the home learning environment was more important for young children’s development than parental occupation, education or income. Analysis of the Millennium Cohort Study has found that the quality of relationships between parents and children are a significant source of variation explaining differences in emotional and behavioural difficulties in children at age 3 [14]. The most recent SEED wave found that higher scores for the home learning environment – which includes activities like reading and play – and warmth of the parent-child relationship were associated with better outcomes on all Early Years Foundation Stage Profile measures [15].   

  4. Parental mental health is closely linked to early childhood inequalities: Analysis of Millennium Cohort Study data shows that children whose mothers have high levels of psychological distress score significantly lower on cognitive tests at age three and are more likely to report socio-emotional and behavioural difficulties [16]. In analysis to understand inequalities in the parent-child relationship, the largest differences are observed in relation to maternal psychological distress, with ‘far lower’ levels of closeness and higher levels of conflict among mothers with high levels of psychological distress. The Born in Bradford study found that while up to 40% of pregnant mums report low mood, very few cases are reported in health data systems. The study also found significant inequalities among ethnic groups, with Pakistani women at greater risk of mental ill health, but half as likely to have a diagnosis recorded with their GP than White British women [17].  

  5. The transformative potential of early childhood education and care: The Perry Preschool Study in the US, which began in the 1960s, identified short- and long-term effects of high-quality preschool education for young children living in poverty, with better high school education outcomes and better rates of employment at age 40 [18]. In the UK, the EPPE study found that pre-school experience enhanced children’s all-round development, with high-quality provision combined with longer duration having the strongest effect on development [19]. Subsequent research of the EPPE cohort found sustained effects on educational outcomes, with those who attended early years education having a greater likelihood of achieving more than 5 GCSEs at grade A-C – with this effect twice as large for children whose mothers had low educational qualifications compared with the whole sample [20]. Recent evidence from SEED has painted a more mixed picture, with some poorer social and emotional outcomes associated with formal early education, especially for young children in group provision for a high number of hours from the age of two [21], providing evidence that the quality and quantity of formal early education are important considerations [22].

The insights provided by longitudinal studies have led to tangible changes in policy and practice to support families with young children. For example, Born In Bradford data found that less than 10% of eligible pregnant women were taking a Vitamin D supplement, with many unaware of the supplement’s importance. Born in Bradford worked with clinicians to promote awareness of and access to Vitamin D supplements during ultrasound appointments, resulting in 97% of women remembering being offered supplements and 87% taking up the offer [23]. Data from the Millennium Cohort Study demonstrated the substantial educational disadvantage of being born at the end of the academic year. This insight led to changes in admissions policy so that parents of children born in late summer could decide which year their child should enter school, depending on the child’s needs.

Challenges of longitudinal studies

While longitudinal studies provide rich insights into the early years, they do face particular challenges and limitations [24]. Longitudinal studies — particularly nationally representative birth cohort studies — are complex and costly. Available administrative data places limitations on sampling of families with young children: identification of nationally representative samples is not currently practicable before children reach nine months of age, limiting our understanding of pregnancy and the earliest months of a baby’s life. Likewise, available data and approaches to sampling and data collection have resulted in “less often heard” populations being under-represented, including babies born into disadvantaged and ethnic minority families — limiting our understanding of these groups’ experiences. 

One specific limitation of existing studies has been a comparatively high focus on mothers rather than fathers, with particular challenges in including non-resident parents. Ensuring longitudinal studies reflect the diversity and complexity of early childhood experiences and development is an ongoing project. The Early Life Cohort Feasibility Study is testing the feasibility of a new nationally representative UK-wide study of babies, with a specific focus on maximising participation of traditionally ‘less often heard’ populations [25].    

Understanding early childhood today:

The Children of the 2020s Study

2022 marks an important milestone in longitudinal studies and the early years, with the launch of the first new nationally representative birth cohort study in England for more than two decades: the Children of the 2020s study [26].

What is the Children of the 2020s study?

The study is a nationally representative birth cohort study of babies born in England. Drawing from HMRC Child Benefit records, approximately 8,500 families have been invited to take part, comprising babies born in September, October and November 2021. The sample will include boosted representation of babies from the most disadvantaged backgrounds. 

The study will include five waves of data collection starting when the cohort of children are 9 months and completing when they are age 5, with the potential for the survey to be extended beyond the age of five, subject to funding. Face-to-face interviews will be part of this, taking place when the cohort children are nine months old and three years old. 

Data collected will look at child development, neighbourhood and family context, family structure, health and mental health, the home learning environment, and formal and informal childcare provision and preschool education. The study also links to both parent and baby Department for Education and NHS digital health records enabling researchers to draw on official information, with parents’ consent.

The study is housed in the Centre for Longitudinal Studies (CLS) at University College London (UCL) and will be led by UCL researchers in partnership with Ipsos and the universities of Cambridge and Oxford and Birkbeck, University of London. The study has been commissioned and funded by the Department for Education (DfE).

The Duchess with Professor Alissa Goodman and Professor Pasco Fearon

Her Royal Highness, The Duchess of Cambridge meets with Professor Alissa Goodman, CLS director, Professor Pasco Fearon, director of the Children of the 2020s study, on a visit to the CLS, 5 October 2021.

What makes the study so exciting?

Part of what makes the Children of the 2020s study so exciting is its timing: coming over 20 years since the last nationally representative study in England, it will provide evidence about early childhood following a period of extraordinary societal and technological change. Since the Millennium Cohort Study, digital technology has become a ubiquitous part of life, with most young children today having access to internet-connected devices [27]. 

The study also comes following what has been an incredibly difficult time for many families with young children, with the study providing invaluable evidence following the COVID-19 pandemic and through the cost of living crisis. As such, the study will provide insights into what may become the “new normal” following the pandemic, such as increased parental working from home, reduced attendance in formal pre-school education, and greater reliance on digital service delivery [28]. The critical need to better understand the experiences of today’s young children is underscored by emerging evidence that the proportion of children achieving a ‘good level of development’ in 2020/21 has fallen 13 percentage points since 2018/19 [29].

“The landmark Children of the 2020s study will illustrate the importance of the first five years and provide insights into the most critical aspects of early childhood, as well as the factors which support or hinder positive lifelong outcomes.”

— Her Royal Highness, The Duchess of Cambridge

What new questions will the study seek to answer?

Critical to the study’s usefulness is its comparability with previous birth cohort studies. Questions have been aligned with past and existing studies, enabling researchers to understand, for example, how inequalities in young children’s development are changing over time.

“This will be an in-depth study of the wide range of factors that affect children’s development and education in the early years, including the home environment, nurseries and preschool, the neighbourhood, early years services and the broader social and economic circumstances of the family. We want to understand how these factors impact children’s social, cognitive, and early language development, their mental health and readiness for school.”

— Professor Pasco Fearon

But the Children of the 2020s will also explore new topics for research. The study will collect information on how parents and young children use technology, with the potential to strengthen the evidence base on how technology affects children’s development and experiences, including parent-child relationships. It will collect more information about fathers and different family forms than previous studies. And it will also collect more information from families about their use of services, with the potential to better inform policymakers about the accessibility and effectiveness of services in meeting the needs of families with young children.

What new methods will the study employ?

One novel aspect of the Children of the 2020s study is its use of an innovative smartphone app called BabySteps. Whereas many previous birth cohort studies have only been able to collect data on an annual basis, BabySteps will allow, at low cost, the research team to collect data more frequently. Participating families will be asked to complete a monthly questionnaire using the app, and have the option to record a range of information — including photos and videos — about their child’s day-to-day experiences. It is hoped that this approach will allow for a more detailed and nuanced understanding of early childhood development, such as language acquisition, and the impacts of aspects of their home environments.

The study also plans to include early years professionals who work with children in the cohort to record their experiences through an app called Teacher Tapp. This has the potential to provide new insights into what quality early education and care looks like.

You can learn more about the Children of the 2020s study at the study’s webpage: https://cls.ucl.ac.uk/cls-studies/children-of-the-2020s-study/


[1] Putting data to work for the early years is one of the six areas of opportunity in the early years identified in our Big Change Starts Small report.

[2] Park, A. and Rainsberry, M. (2020). Introduction to longitudinal Studies. CLOSER.

[3] Belsky, J., Caspi, A., Moffitt, T. E., and Poulton, R. (2020). The Origins of You: How Childhood Shapes Later Life. Harvard University Press.

[4] Centre for Early Childhood. (2021). Big Change Starts Small. Royal Foundation.

[5] Drawing on the Millennium Cohort Study and 1970 British Cohort Survey: Cattan, S., Fitzsimons, E., Goodman, A., Phimister, A., Ploubidis, G. B., and Wertz, J. (2022). Early childhood inequalities. IFS Deaton Review of Inequalities. IFS.

[6] Belsky, J., Caspi, A., Moffitt, T. E., and Poulton, R. (2020). The Origins of You: How Childhood Shapes Later Life. Harvard University Press.

[7] Cattan, S., Fitzsimons, E., Goodman, A., Phimister, A., Ploubidis, G. B., and Wertz, J. (2022). Early childhood inequalities. IFS Deaton Review of Inequalities. IFS.

[8] Drawing on the Millennium Cohort Study: Cattan, S., Fitzsimons, E., Goodman, A., Phimister, A., Ploubidis, G. B., and Wertz, J. (2022). Early childhood inequalities. IFS Deaton Review of Inequalities. IFS.

[9] Ibid.

[10] Ibid.

[11] Sylva, K., Melhuish, E., Sammon, P., Siraj-Blatchford, I. and Taggart, B. (2004). Technical Paper 12. The Final Report: Effective Pre-School Education. London: UCL Institute of Education, p14.

[12] Cattan, S., Fitzsimons, E., Goodman, A., Phimister, A., Ploubidis, G. B., and Wertz, J. (2022). Early childhood inequalities. IFS Deaton Review of Inequalities. IFS.

[13] Melhuish, E. C. and Gardiner, J. (2020). Study of early education and development (SEED): Impact study on early education use and child outcomes up to age five years. Department for Education.

[14] Cattan, S., Fitzsimons, E., Goodman, A., Phimister, A., Ploubidis, G. B., and Wertz, J. (2022). Early childhood inequalities. IFS Deaton Review of Inequalities. IFS.

[15] https://borninbradford.nhs.uk/wp-content/uploads/Key-Findings_FINAL_Designed.pdf

[16] https://image.highscope.org/wp-content/uploads/2018/11/16053615/perry-preschool-summary-40.pdf

[17] Sylva, K., Melhuish, E., Sammon, P., Siraj-Blatchford, I. and Taggart, B. (2004). Technical Paper 12. The Final Report: Effective Pre-School Education. London: UCL Institute of Education.

[18] Cattan, S., Crawford, C., Dearden, L. (2014). The economic effects of pre-school education and quality. London: IFS.

[19] Melhuish, E. C. and Gardiner, J. (2020). Study of early education and development (SEED): Impact study on early education use and child outcomes up to age five years. Department for Education.

[20] Archer, N. and Oppenheim, C. (2021). The role of early childhood education and care in shaping life chances. Nuffield Foundation.

[21] See https://learning.closer.ac.uk/learning-modules/introduction/what-can-longitudinal-studies-show-us/weaknesses-of-longitudinal-studies/

[22] See https://cls.ucl.ac.uk/cls-studies/early-life-cohort-feasibility-study/

[23] The author would like to thank Pasco Fearon for his time in speaking about the study, which forms the basis of this section.

[24] Batcheler, R., Ireland, E., Oppenheim, C., Rehill, J. (2022). Time for parents. Nuffield Foundation.

[25] Oppenheim, C. (Forthcoming). Bringing up the next generation: from research to policy. Nuffield Foundation.

[26] Tracey, L., Bowyer-Crane, C., Bonetti, S., Nielsen, D., D’Apice, K. and Compton, S. (2022). The impact of the Covid-19 pandemic on children’s socio-emotional wellbeing and attainment during the reception year. Education Endowment Foundation.