MQSUN⁺ provides global demand-driven short-term technical assistance (STTA) to country governments in the Scaling Up Nutrition (SUN) Movement. The project aims to translate our monitoring and evaluation (M&E) results into applied lessons learnt to improve the efficiency and effectiveness of future STTA and SUN country efforts.  MQSUN⁺ developed a methodology to assess the impact of STTA on the capacity and “power” of countries to take forward their scaling up nutrition agenda. As part of this, MQSUN⁺ utilises an assumptions map to test our theory of change for STTA impact. This forms the basis of retrospective analysis of country-based case studies. Given the growing role of STTA in international development, this methodology and corresponding case studies can offer lessons and facilitate discussion on M&E of STTA mechanisms.