Child and adolescent development is influenced by complex interplay between a range of diverse factors. The network approach is gaining popularity as a way of modelling such complex processes. Here we used the network approach to investigate whether developmental differences and disorders can be conceptualised as arising from interactions between characteristics and symptoms. We used data from four population-based birth cohorts in England (n = 47,315), those born in the 1970s, 1990s and 2000s, to investigate interrelations between areas of psychological functioning that underpin learning and engagement in education settings (i.e., memory, attention, non-verbal ability, arithmetic skills, reading, language and communication, motor skills, neurodevelopmental characteristics, psychopathology, social functioning and wellbeing). We fitted 12 undirected psychometric network models; one network for each cohort and developmental stage (early childhood; 3-5 years, middle childhood; 7-10 years, adolescence; 13-18 years). We then determined how these areas of functioning cluster within developmental domains. In early and middle childhood, psychological functioning, generally, clustered within two related developmental domains: (1) cognition and language and (2) social and emotional functioning. In adolescence, they clustered within three developmental domains (1) cognition and language and (2) social functioning and (3) emotional functioning. We demonstrate that developmental differences and disorders can be conceptualised through the network modelling approach. One possibility requiring further investigation is that they arise through bottom-up processes, whereby a given symptom or characteristic activates or leads to another; symptoms or characteristics that activate or lead to each other cluster together and appear as neurodevelopmental or psychiatric conditions. Differences and disorders that appear to be similar, prima facie, may be underpinned by diverse etiologies. Our work provides the first population-level evidence for a needs-based support system in schools; children and adolescents with developmental disorders and differences should be supported by targeting specific characteristics and symptoms. Such an approach does not rely on waiting for a diagnostic assessment through lengthy processes. SUMMARY: Developmental differences and disorders likely arise through complex interactions between different areas of psychological functioning in a bottom-up manner. Differences and disorders that appear to be similar, on the face of it, may have distinct causes; no single causal factor is necessary nor sufficient.