New UW–Madison, MMSD Journal Article Finds Preschoolers Already Form Friendships Based on Shared Characteristics
June 18, 2026 | By Katie Grant, Office of Research & Scholarship Communications
New research, published in a peer-reviewed journal by researchers from the University of Wisconsin–Madison and the Madison Metropolitan School District (MMSD), shows that children as young as 4 years old begin forming social networks shaped by shared characteristics, offering new insight into how early peer relationships develop.
The study, published in Early Childhood Research Quarterly, examines how preschool students choose their playmates and whether those choices reflect “homophily” — the tendency to associate with others who are similar. Using data from nearly 400 children in MMSD’s 4-year-old kindergarten (4K) program, researchers found that even at this early age, children show clear patterns in their playmate choices.
“The preschool years are a critical time when children begin forming stable peer relationships and developing the social and cognitive skills needed to engage with others,” the study’s authors, Rebecca Bier, Elizabeth Vaade, and Culleen Witthuhn, write. The findings suggest that these early interactions may lay the groundwork for how friendships later form.
The research analyzed peer networks across 28 classrooms during the 2021–2022 school year, drawing on teacher reports about which classmates children played with most frequently, as well as administrative and assessment data. Classrooms were relatively diverse in terms of race, socioeconomic status, and academic skills, giving students opportunities to interact with a wide range of peers.
The study found that children were about 23 percentage points more likely to choose to play with classmates of the same sex than peers of a different sex, making it the strongest predictor of friendship patterns in the classroom. Other characteristics were also predictive of peer relationships, though to a lesser degree. Children showed modest tendencies to play with peers who shared similar socioeconomic backgrounds — measured in this study through free or reduced-price lunch eligibility and parent education — and similar race or ethnicity. Each of these factors increased the likelihood of being playmates by roughly five to six percentage points.
Researchers also observed clustering among children with shared learning or developmental characteristics. Students with special education designations were about 11 percentage points more likely to play with peers who had similar designations. There were weaker tendencies for children to play with peers who had similar English language proficiency or early literacy skills.
In contrast, age differences within the classroom did not significantly influence friendships.
Implications for Early Learning and Classroom Practice
Because preschool classrooms often emphasize play-based learning, peer interactions are a central part of children’s daily experience. Prior research shows that these interactions are critical for developing cooperation, communication, and social understanding.
The study suggests that while some degree of homophily emerges naturally, preschool settings may also offer unique opportunities to foster diverse friendships, especially since patterns based on race and socioeconomic status appear weaker than those observed among older students.
“Understanding how and when children begin to form these preferences may help educators design environments that foster inclusive and diverse peer interactions,” said Bier, a Ph.D. student in sociology at UW–Madison, co-author of the study, and fellow in the Interdisciplinary Training Program in Education Sciences (ITP) at the Wisconsin Center for Education Research (WCER). “This research highlights the importance of intentionally supporting opportunities for young children to engage with a wide range of peers early in their educational experiences.”
The findings are particularly relevant for school districts that prioritize belonging, cultural competence, and social-emotional development.
“This work gives us valuable insight into the social dynamics already taking shape in our classrooms,” said Vaade, Senior Executive Director of Research, Assessment, and Improvement for MMSD and co-director of the Madison Education Partnership (MEP) at WCER. “It underscores both the strengths of our diverse preschool environments and the opportunity we have to intentionally support meaningful connections across differences.”
The authors note that while homophily is well documented in middle and high school settings, far less is known about how early these patterns begin. This study helps fill that gap by demonstrating that social sorting is already present in preschool but not yet as entrenched as it becomes later.
That distinction matters. Early childhood may represent a critical window when interventions to promote cross-group friendships could have lasting benefits. Research suggests that interacting with diverse peers can foster empathy, reduce bias, and support both social and academic development.
“At this stage, peer groups are still relatively fluid, and children are engaging with a broader range of classmates than we often see in later grades,” the researchers conclude. “This creates important opportunities for educators and policymakers to support inclusive peer environments from the very start of schooling.”
Read the full article in Early Childhood Research Quarterly’s 3rd Quarter 2026 issue.
About the Madison Education Partnership (MEP)
MEP researchers mutually define and investigate problems relating to student learning, equity, and district-wide concerns, then collaboratively identify responsive policies and solutions based on results. For more information, visit mep.wceruw.org.
About the Wisconsin Center for Education Research (WCER)
WCER at UW–Madison’s #1-ranked School of Education is one of the world’s oldest and most productive education research centers. WCER has supported researchers and scholars in developing, submitting, conducting and sharing grant-funded education research for over 60 years. See wcer.wisc.edu for additional information.
