Just as youth development has evolved to mean more than the treatment of already-present problem behaviors, so there has been some oscillation between prevention and intervention.

Intervention programs, seeking mainly to address existing crises, predated prevention programs by some two decades (Catalano 99). However, in the last ten to fifteen years, concurrent with the emergent emphasis on positive youth development, the idea of prevention programs has become an important facet of youth development. In Roth’s study, fully 92% of the programs purported to feature activities aimed at the prevention of high-risk behaviors. Nonetheless, youth development advocates now “recognize that activities focused solely on the prevention of problem behaviors, such as violence or substance abuse, do not necessarily equip adolescents with the tools for a responsible and productive adulthood” (Roth, 97). Prevention programs, as opposed to intervention programs, are designed to change youths' projected life course, either by adding competency, experience, interactions, or some other ingredients.

Implicit in the discussion of prevention and intervention is the notion of critical periods. Also known as sensitive or etiological periods, these are the stages of development or ages when identity is formed, and risk and protective factors are most influential. By extension, critical periods also represent the most opportune or beneficial times for staging interventions or experiencing prevention programming. Researchers have developed various life course paradigms, which posit and chart when these critical periods occur. Berkman discusses three (33-36).

The first is the latency model, which is based on "critical or sensitive periods in which early childhood or even prenatal exposures shape subsequent outcomes that may or may not be evident for years" (33). This model is supported by experiments with rats--some handled and some not handled in early life. The rats in the two groups remained similar in behavior and development until midlife/older age, when "the nonhandled rats developed significant cognitive impairment and simultaneously had higher levels of corticosterone"(34) (corticosterone is one of those "stress hormones" diet supplement commercials are always pestering us about).
       The second life course paradigm is cumulative exposure, based on the idea that, in the absence of critical periods, life experiences simply have a cumulative effect, so repeated exposure to something would cause significant shaping of behavior or development (33). This model is supported by empirical evidence from studies that link prolonged periods of economic disadvantage to increased risk of disease, for example heart disease (35). It's important to note that the cumulative exposure paradigm "argues that changes in adulthood to modify risk or prevent the onset of risk will partially offset the risks set by trajectories in early childhood (35).
       The final model in Berkman's paper is social trajectory, which contends "that early life exposures do not directly affect adult health. They influence adult social conditions, which, in turn, affect adult health. In this case, intervention in adulthood can completely offset harm incurred in childhood" (36). An example of this paradigm is related to occupational hazards. Early life experiences, such as education and class, put people on the track to more or less hazardous jobs, which results in more or less exposure to contaminants, risk of death, stress, etc. These risks can be undone with an adult intervention to change the workplace (36).