The Atlas Transformation Language (ATL) is today a de-facto standard in model-driven development. It is understood by the community that methods for exhaustively verifying such transformations provide an important pillar for achieving a stronger adoption of model-driven development in industry. In this paper we propose a method for verifying ATL model transformations by translating them into DSLTrans, a transformation language with limited expressiveness. Pre- / postcondition contracts are then verified on the resulting DSLTrans specification using a symbolic-execution property prover. The technique we present in this paper is exhaustive for the declarative ATL subset, meaning we are certain that if a contract holds, it will hold when any input model is passed to the ATL transformation being checked. We explore the scalability of our technique using a set of examples, including a model transformation developed in collaboration with our industrial partner.