This paper examines the use of national microsimulation models in a cross-country context and highlights some of the difficulties associated with carrying out comparative research. Changes to the equivalence scales of social assistance systems in favour of children in Germany, Ireland and the UK were modelled. Unlike a number of previous studies of this kind, reforms were modelled in the policy and societal context in which the reforms are set. To do this, three national tax-benefit microsimulation models were used. The analysis highlighted both the different structure of the policy instruments used across the countries, but also the importance of the national environments in which the policy is set.