What does the MDI measure?

A guide to the dimensions and indices of the MDI

Middle childhood is a time in development that is complex and multifaceted. The Middle Years Development Instrument (MDI) is designed to capture this complexity and provide a holistic picture of how children in the middle years are doing at school, at home, and community. The MDI provides valid and reliable information on children in the middle years on five key dimensions: Social and Emotional Development, Physical Health and Well-Being, Connectedness, Use of After-School Time, and School Experiences. Understanding the importance of each of these five dimensions, their roles in supporting positive development during the middle years, and exploring the ways in which these dimensions are interrelated serves as an important foundation for understanding and interpreting MDI data.

Social and Emotional Development

The development of social and emotional skills, including empathy, optimism and self-esteem, are important for supporting positive mental health during middle childhood and at all ages to follow.

Physical Health and Well-Being

Promoting children’s physical health and well-being in the middle years lays the foundation for a healthy life.


Strong and supportive social connections play an important role in children’s healthy development. 

Use of After-School Time

Participation in activities after school provides important developmental experiences for children in their middle years.

School Experiences

Children’s school experiences are important for their personal well-being and academic success.

In addition to the data provided on each of the MDI dimensions, the MDI also provides two summary indices that provide a comprehensive summary on how children are doing in the middle years: 

The Well-Being Index

The Well-Being Index provides a holistic summary of children’s social, emotional, and physical health. 

The Assets Index

Adult Relationships

After-School Activities

Peer Relationships

Nutrition & Sleep

The Assets Index provides a quick summary of components or qualities present in children’s lives that are foundational to their well-being.