Proponents of ecosystem services approaches to assessment claim that it will ensure the environment is 'properly valued' in decision making. Analysts seeking to understand the likelihood of this could usefully reexamine previous attempts to deploy novel assessment processes in land-use planning and how they affect decisions. This paper draws insights from a meta-analysis of three case studies: environmental capital, ecological footprinting, and green infrastructure. Concepts from science and technology studies are used to interpret how credibility for each new assessment process was assembled, and the ways by which the status of knowledge produced becomes negotiable or prescriptive. The influence of these processes on planning decisions is shown to be uneven, and depends on a combination of institutional setting and problem framing, not simply knowledge content. The analysis shows how actively cultivating wide stakeholder buy-in to new assessment approaches may secure wider support, but not necessarily translate into major influence on decisions.