Why Growing Up Matters for Mental Health

An in-depth, plain-language summary of new research on youth development, mental health, and personality functioning

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Unravelling the Longitudinal Relations Between Developmental Milestones, General Psychopat.

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Adolescence and emerging adulthood are often described as periods of growth, exploration, and opportunity. For many young people, however, these years are also marked by emotional suffering, psychological distress, and difficulties finding their place in the world. A recent longitudinal study published in the Journal of Youth and Adolescence takes an in-depth look at how three fundamental dimensions of youth development are interconnected: psychopathological symptoms, personality functioning, and the achievement of developmental milestones.

Rather than examining these factors in isolation, the researchers posed a simple but crucial question: How do these aspects of development influence one another over time? The findings offer important insights for clinicians, parents, educators, and anyone concerned with youth mental health.

Three key concepts explained simply

Before turning to the results, it is useful to clarify the three core concepts at the heart of the study.

1. General psychopathology

General psychopathology refers to overall psychological distress. Instead of focusing on a single diagnosis (such as depression or anxiety), the study considers a broad range of emotional and behavioral symptoms. This approach better reflects clinical reality, where many young people experience overlapping and shifting difficulties rather than clearly defined diagnostic categories.

2. Personality functioning

Personality functioning describes how a person understands themselves and relates to others. It includes two broad domains:

• Self-functioning, such as identity stability and the ability to set and pursue goals;

• Interpersonal functioning, such as empathy, intimacy, and the capacity to maintain meaningful relationships.

Importantly, impairments in personality functioning are not limited to personality disorders. They can be present, to varying degrees, across many forms of psychopathology.

3. Developmental milestones

During adolescence and emerging adulthood, young people are expected to reach certain age-normative developmental milestones. These include:

• Building friendships and peer relationships (social domain),

• Developing autonomy and a coherent sense of identity (personal domain),

• Managing school, education, or work responsibilities (educational and vocational domain).

Persistent difficulties in these areas can make everyday life particularly challenging and may indicate that developmental progress is being disrupted.

How the study was conducted

The researchers followed 525 young people aged 12 to 26 who were receiving outpatient mental health care in the Netherlands. Most participants were experiencing significant psychological difficulties and were assessed at three time points over the course of one year.

At each assessment, participants completed questionnaires measuring:

• Levels of psychological distress,

• Personality functioning,

• Difficulties in achieving age-appropriate developmental milestones.

Thanks to the longitudinal design, the researchers were able to examine not only whether these factors were associated, but also which preceded the others over time.

What the findings show

1. The three dimensions are closely linked

At every assessment point, the same pattern emerged:

• Young people with higher levels of general psychopathology also showed greater impairments in personality functioning;

• Both were associated with greater difficulties in achieving developmental milestones.

In short, when one domain was compromised, the others tended to be as well.

2. These difficulties are not fixed

Although all three domains showed moderate stability across six-month intervals, they also changed over time. This is an important and encouraging finding, as it suggests that adolescence and emerging adulthood remain periods of psychological plasticity, even among clinically referred youth.

Treatment, life events, and developmental opportunities can all alter developmental trajectories. Difficulties in personality functioning or developmental progress are therefore not fixed destinies.

3. Developmental milestones as a predictive factor

The most theoretically significant finding concerns the direction of effects over time. Difficulties in achieving developmental milestones predicted subsequent worsening in personality functioning six months later. The reverse effect did not emerge.

This indicates that everyday functioning in real-world contexts—school, work, relationships, and autonomy—is not merely a consequence of pre-existing personality difficulties, but may actively contribute to shaping personality development.

Taking a closer look: why these processes are connected

To understand the central role of developmental milestones, it is important to consider what this life stage actually demands. Adolescence and emerging adulthood are not only about emotional regulation or symptom reduction; they are about learning how to live in the world.

Young people are expected to experiment with roles, negotiate autonomy from caregivers, build reciprocal relationships, and gradually assume educational or vocational responsibilities. These experiences form the foundation of adult psychological functioning.

When these developmental tasks are repeatedly experienced as difficult or unsuccessful, young people may develop identity uncertainty, impaired self-direction, and difficulties with trust in relationships. Over time, such experiences can undermine the development of healthy personality functioning.

Why personality functioning matters beyond diagnoses

One of the study’s strengths is its focus on personality functioning rather than categorical diagnoses. Traditional diagnostic labels often fail to capture the complexity of young people’s clinical presentations, which are characterized by comorbidity and change over time.

Personality functioning, by contrast, captures how a person functions psychologically: the coherence of the self, the capacity for goal-directedness, empathy, and the quality of interpersonal relationships. The findings suggest that strengthening these core capacities is just as important as reducing symptoms.

Stability and change: what the longitudinal design reveals

Following participants over time made it possible to distinguish between continuity and change. Young people who struggled at one time point often continued to struggle six months later, but with meaningful room for improvement or deterioration.

This confirms that adolescence and emerging adulthood are periods of heightened malleability, during which targeted interventions can meaningfully influence developmental trajectories that might otherwise become entrenched.

Rethinking clinical intervention priorities

The findings suggest a shift in how youth mental health interventions are conceptualized. Rather than waiting for symptom reduction before encouraging engagement in school, work, or social life, it may be beneficial to actively support developmental engagement as part of treatment itself.

This may involve:

• Supported re-entry into school or work,

• Structured opportunities for peer interaction,

• Interventions targeting autonomy and daily living skills,

• Family-based work that balances protection with independence.

Implications for prevention

The implications extend beyond clinical settings. If difficulties in developmental milestones can precede and predict later impairments in personality functioning, early identification becomes crucial.

Schools, community services, and primary care providers are well positioned to notice early warning signs such as social withdrawal, identity confusion, or disengagement from education, and to intervene before these difficulties solidify.

A developmental perspective on youth mental health

Taken together, the findings highlight the value of a developmental perspective on mental health. Adolescence and emerging adulthood are not only periods when symptoms emerge, but also windows of opportunity.

Supporting young people in mastering everyday developmental tasks may contribute not only to symptom reduction, but also to the formation of a healthier personality structure and more adaptive adult functioning.

In this sense, the study conveys a hopeful message: helping young people move forward in life may also help them heal psychologically.