I'm not sure where to start with this. First of all -- and luckily for you -- spelling has nothing to do with being gifted. Different organizations and school systems have varying benchmarks for students to be tagged as gifted. A very general guideline would be the 98th percentile (only the 99th percentile is higher -- there is no 100th percentile). On the CoGAT tests this is 132, on the NNAT or Naglieri this is 130. Some say that in order to be "highly gifted" you need to be over 140. Some programs take scores as low as 120 as the benchmark. Please know that many other factors are typically used as well -- grades, other standardized tests, teacher comments, and something called a GBRS or Gifted Behavior Rating Scale. Finally, another important point to address in your question. Grade or age has nothing to do with an IQ score. Theoretically, a person testing at 136 in Kindergarten would have the same scores at 10, 15, 30 and even 50 years old. I hope that helps answer all your questions.
According to SOWPODS (the combination of Scrabble dictionaries used around the world) there are 1 words with the pattern ---NNAT. That is, seven letter words with 4th letter N and 5th letter N and 6th letter A and 7th letter T. In alphabetical order, they are: quinnat