Understanding about what constitutes development effectiveness requires elaboration in order for evidence to add greater value. Development in the twenty-first century is often complicated, if not complex, and correspondingly is most likely to be achieved through diagnostic, contextual approaches to experimentation and innovation. Impact planning, assessment, reporting, and learning systems (IPARLS) can successfully contribute to development effectiveness because they integrate key lessons learned about both the more successful generation and utilisation of evidence, and are aligned with the nature of twenty-first century development. Impact evaluations should be embedded in IPARLS in order to be more legitimate and better used. The systematic application of comparison and triangulation is the platinum standard of rigour for impact evaluations. Impact evaluations can be further improved if they are theory-based, investigate descriptive and causal inference, analyse casual mechanisms, and focus on contextual elaboration. Case and comparative case study designs for impact evaluation remain essential and these approaches can be made more rigorous given recent methodological advances. Impact evaluations and IPARLS will and should be judged by their contribution to greater understanding of development effectiveness and ultimately improved development.
