Abstract-Computational GRIDs potentially offer low-cost, readily available, and large-scale high-performance platforms. For the parallel execution of programs, however, computational GRIDs pose serious challenges: they are heterogeneous and have hierarchical and often shared interconnects, with high and variable latencies between clusters. This paper investigates whether a programming language with high-level parallel coordination and a Distributed Shared Memory (DSM) model can deliver good and scalable performance on a range of computational GRID configurations. The high-level language Glasgow parallel Haskell (GpH) abstracts over the architectural complexities of the computational GRID, and we have developed GRID-GUM2, a sophisticated grid-specific implementation of GpH, to produce the first high-level DSM parallel language implementation for computational GRIDs. We report a systematic performance evaluation of GRID-GUM2 on combinations of high/low and homogeneous/heterogeneous computational GRIDs. We measure the performance of a small set of kernel parallel programs representing a variety of application areas, two parallel paradigms, and ranges of communication degree and parallel irregularity. We investigate GRI D-GUM2's performance scalability on medium-scale heterogeneous and high-latency computational GRIDs and analyze the performance with respect to the program characteristics of communication frequency and degree of irregular parallelism.