There are definite differences between the Raven's Progressive Matrices and the Cognitive Ability Test. The Raven is a non-verbal test of reasoning based on visual stimuli. It measures the ability to form comparisons, to reason by analogy, and to organize spatially. It is also an older test and not used widely in all school districts as a measure of giftedness. Currently, entry into gifted programs is often based on verbal skill abilities. This would not be measured on the Raven. It is possible to obtain a factored score that is considered a valid indicator on the Cognitive Ability Test even if the non-verbal section is not administered. Evidently your son's testing in Colorado put a heavier emphasis on verbal skills.
Now here is what you need to find out: What tests are accepted in your state and school district as measures of giftedness? Will the district accept private psychological testing, if you choose to obtain it, for qualifying into the gifted program? A student who has done well in a gifted program for three years deserves another look to see if local gifted programs can benefit him.