I took a "test one test all" approach but mainly as I have twins and you tend to do that sort of thing with same age siblings. We were expecting one to test gifted and one "just bright" and we were both very convinced we were right--> turns out they both had matching WISCIV scores and both highly gifted but with differing personalities (which is where the confusion came in, one has a "can't be bothered" personality, the other "tries and tries until gets 100%" type approach). We tested at age 6.