Young people are surrounded by many peers in their daily lives. One of the most important topics in adolescent development is peer influence among adolescents. But which peers influence what? A paper by Mary Page Leggett-James, René Veenstra, Goda Kaniušonytė and Brett Laursen answers part of that question. The authors directly compare the influence of best friends with that of classroom norms more closely related to popularity.

What exactly did they do? In a sample of 543 Lithuanian students (aged 10–14), they looked over a three-month period at changes in:

• emotional problems

• lack of emotional clarity

• problem behaviour

• academic performance

• social media use

• weight concerns

They used a fairly sophisticated analytical technique (a longitudinal Group Actor-Partner Interdependence Model) that allows researchers to estimate the unique influence of best friends and status norms simultaneously, while filtering out overlapping effects.

The first lesson: best friends mainly influence what makes you vulnerable. More emotional problems in your best friend predict more emotional problems in you. This fits with earlier research, as far as I remember. The same applies to lack of emotional clarity and problem behaviour. Among older students, best friends also influence academic performance.

Popularity, on the other hand, mainly influences what is visible. When popular students spend a lot of time on social media, classmates’ social media use increases. Among older students, the same holds for weight concerns: when popular students are preoccupied with it, concern about weight increases across the class.

The authors frame this through two social “algorithms”. In friendships, reciprocity is the key principle. You adapt to maintain the relationship. This happens in a relatively safe and private sphere. It is therefore not surprising that internalising problems and shared difficulties spread there. Think of co-rumination: worrying together can create connection, but it can also reinforce problems.

In groups, hierarchy plays a larger role. Popular students model what brings status. And status is visible. Think of things like appearance, social media, or public impressions.

What I like about this study is that it punctures a simplification we often make. We talk about “peer pressure” as if it were a single mechanism, as if all peers push in the same direction. This research shows that the reality is more nuanced. If you want to understand problem behaviour, look at best friends. If you want to understand social media use or appearance norms, look at popular students.

This also has implications for interventions. If you want to address behavioural problems, changing classroom norms alone will not be enough. You need to look at friendship networks. Who sits next to whom? Which dyads reinforce each other?

If you want to temper social-media use or appearance pressure, the primary focus should not be individual counselling but norm change. And norm change runs through status holders. Without getting popular students on board, little will change.

As with any study, there are also limitations. The sample comes from Lithuania, although the authors argue that the context is comparable to other Western European settings. The measurement period is relatively short. Small effects may remain under the radar. But methodologically, this is strong work, precisely because it models both influences simultaneously.