An under-appreciated method for partitioning data into training and test

Perhaps one of the most under-appreciated tools in ArcGIS is subset features. While there are numerous examples of how to generate random points, which can then be sorted and used to generate fields for subsetting your data why not just do it directly? The subset features tool in the Geostatistical Analyst toolbox does this. Another alternative to check out is the Marine Geospatial Ecology Tools. MGET has numerous tools for doing modeling and is a great resource for quickly running models and bring the results back into ArcMap for display.