The disqualification of urban plans to provide formal settlements for the new population caused the growth of informal settlements. The main lesson learned in terms of increasing the realisation level of similar participatory projects and processes to the 'Iran Urban Upgrading and Housing Reform Project' is that the project preparation and design phase is more important than other phases. After an overview of the project's objectives and beneficiaries, it is necessary to specify the key factors in project progress and the outcomes of the evaluation process in order to be able to have a more reliable and regular evaluation. These key factors can be divided into five categories referring to last World Bank report and according to their scale and realisation phase. They are key factors relevant to the project preparation, design and quality at entry, project implementation, project monitoring and evaluation (M & E) design, implementation and utilization, the project safeguard and fiduciary compliance and the project post-completion operation.