This article engages with diachronic analysis, an analysis of changes over time, as it relates to the field of language planning and policy (LPP) through a case study of a local language problem: the introduction of Chinese language into an established government school over a 10-year period. Using cultural-historical activity theory, expanding learning cycles unfold over time to reveal "how" activity systems create, maintain, and resolve cyclical (re)iterations of the problem, in this case, of moving towards and away from the implementation of Chinese as a new language programme within the school. The intersection of the domains of cultural-historic time (the changing sociocultural context within which the language planning problem is situated), ontogenetic time (the development of decision-makers and their identity across their life spans), and microgenetic time (instances in LPP activity at the level of concrete engagement) show "why" policy is produced, (re)shaped, and enacted in practice. The case study illustrates that LPP is a "messy" social process necessarily dependent on contradictions and tensions rather than being rational, technical, and linear.