Rigorous impact assessments test for causal effects of interventions on outcomes of interest. When findings of such assessments become part of political and scholarly controversies, they can be interpreted in unintended ways. The value of the ensuing debate is enhanced by a shared understanding of key concepts, methodological approaches, and evaluative criteria. Here we illustrate the importance of such shared understanding by example of a recent controversy surrounding the estimated impacts of decentralized zoning on deforestation in a major agricultural frontier, the Argentine Dry Chaco. In a recent analysis, we concluded that provincial zoning plans had significantly reduced deforestation in three provinces; critics suggest it had not. In attempting to resolve this debate, we identify six areas in which shared understanding can support more productive interaction. These include: (1) the distinction between impact and other measures of effectiveness, (2) an appreciation of recent advances in methods for causal inference, (3) the distinction between effective and perfect enforcement, (4) the challenge of attributing impacts to mechanisms and actors, (5) transparency in standards used to judge the desirability of observed outcomes, as well as (6) caution in the generalization of findings to other geographies.