Sometimes, it takes more than a strong start—it takes a start that lasts. That thought came to me after reading a new longitudinal study in Child Development, tipped to me by my wife (thanks!). The study followed a group of children for no less than 14 years—yes, from preschool all the way through high school—to ask a deceptively simple question: Can a well-designed preschool intervention make a difference that long?

The answer, surprisingly, is yes—but not necessarily in the ways you might expect.

The REDI project (short for Research-based, Developmentally Informed) added a structured social-emotional learning (SEL) curriculum to existing Head Start classrooms. Think of daily activities around naming emotions, practising self-control, interactive reading sessions with SEL themes, and even handouts and DVDs for parents. The target group: 4-year-olds from low-income families in Pennsylvania. The comparison group? Peers in “business-as-usual” Head Start classrooms.

Fast-forward to high school. The kids who underwent REDI showed significantly fewer emotional problems (effect size d = 0.41) and behaviour problems (d = 0.27). These are not earth-shattering numbers, but they’re remarkable for a universal classroom intervention done more than a decade earlier. No direct effects were found for GPA or graduation—but here’s the twist: indirect effects were found, via reductions in behavior problems and improved relationships with teachers and parents in primary school.

That’s what makes this study stand out. It’s not just a “did it work?” design. The researchers mapped the whole causal chain: preschool SEL → better social adjustment in elementary school → fewer emotional/behavioural issues in high school → better academic outcomes. In other words: developmental cascades in action.

It also highlights an essential nuance in the often-heard debate about “fade-out” effects in early education. Yes, the vocabulary and phonemic awareness gains from REDI faded quickly. But the social-emotional boosts? Those stuck. And they mattered in the long run, especially for adolescents growing up in challenging contexts.

So what should we take away from this?

First, not all preschool interventions are created equal. This one costs about $191 per child, not a massive investment compared to what’s at stake. Second, the real payoff of early intervention might not be in early test scores, but in long-term well-being and adjustment. And third, if you’re going to design something for the early years, make sure it’s good enough to echo into adolescence.

Sometimes, what lasts longest isn’t the academic boost, but the emotional compass we give children when they’re four.

Abstract of the study:

This study examined the impact of the Head Start Research-based, Developmentally Informed (REDI) preschool intervention on high school outcomes and explored longitudinal mediation. 356 children (58% White, 25% Black, 17% Latinx; 54% female, 46% male; M_age = 4.49 years) were recruited from Head Start classrooms which were randomized to intervention (N = 192) or “usual practice” (N = 164). REDI effects emerged on high school emotional symptoms (teacher ratings, d = 0.41) and behavior problems (composite of teacher, parent, youth ratings, d = 0.27) with the latter benefits mediated by earlier intervention boosts to social–emotional learning, social adjustment, and parent involvement. REDI had no direct impact on GPA or on-time graduation but promoted these outcomes indirectly mediated by earlier intervention effects.