In the last few years, non-governmental organizations (NGOs) have accepted the responsibility of assessing their own impact to determine what actions and policies positively affect people's lives. Many organizations have developed tools and good practices in this regard. NGOs in the field of international development began this journey several years ago, however, human rights groups have been slower in the tast. For example, Amnesty International formally adopted in 2008 the same impact assessment methodology Dimensions of Change that Save the Children has been working with since at least 2003. This paper follows the comparative method of "Most Similar Systems Design" (MSSD). It compares different outcomes across similar units. The paper begins with a short presentation of the debate regarding the necessary conditions for a successful NGO and impact assessment as a matter of accountability. The paper will also present the progressive intersections between development and human rights NGOs, and, finally, it will explain why development organizations have advanced more than human rights organizations in the assessment of their own impact. This essay focuses on common patterns observed among development and human rights NGOs, with less emphasis on the differences.