In many parts of the world, governments are building new platforms, methods, and innovative experimental spaces to better respond to current complex problems. Laboratories in the public sector have emerged as experimental spaces that incorporate co-creation approaches to promote public innovation and social transformation. Although there is abundant literature about public innovation and reports on innovative practices, little progress has been made on how to evaluate these. In this paper, we describe the process that led to the development of an experimental evaluation tool for public innovation as part of an action-research process in a laboratory within the Uruguayan Government. The pilot prototype, the 'Roadmap' as we named it, seeks to provide a timely and purposeful means to learn from the co-creation processes and be accountable to public authorities and society. Aiming to build a learning system within the organisation to communicate results, we designed the Roadmap based on the confluence of various approaches, namely, development evaluation, organisational learning and reflexive monitoring. Other relevant approaches to public innovation and evaluation were also considered, such as public design evaluative thinking, social innovation evaluation, and systemic evaluation of learning.