Youth is commonly conceptualised as a period of transition in which young people strive to meet the social markers of adulthood, such as getting work, starting families and being recognised as full and productive citizens. Here we extend our analysis of youth to capture the developmental needs of young people in this process of 'becoming'. In doing so we explore the literature on developmental psychology and youth well-being that has been well explored in the Global North, but less so in the Global South. From this, we highlight that development studies must look more broadly at the developmental processes occurring through youth of building foundations, building blocks, building support structures and building dreams. Young people's current and future outcomes cannot be understood fully without understanding these processes, which are critical behavioural drivers. We then move on to explore the literature on urban youth in Sub-Saharan Africa to assess whether or not these four critical developmental processes are accessible to young people in Sub-Saharan Africa's towns and cities. The literature recognises the difficulties urban youth in Sub-Saharan Africa face in navigating these pathways and the subsequent 'transitional limbo' they themselves in. Urban areas characterised by weak job creation, informality and tough competition offer few social and economic opportunities to young people. We draw upon our earlier review of literature from developmental psychology to explore the implications of this on young people's development. At such a formative stage in the life cycle it leads to crises in personal identity formation and prevents the development of important internal developmental assets (like self-confidence and self-belief) that young people need to thrive and flourish. Urban poverty and processes of urban social change have also eroded the social support systems necessary to nurture these vital assets. Together these dampen and constrain young people's ability to envision, strive for and plan to meet opportunities today and into the future.