I am not sure that SET will solve your DC's issues. SET is a recognized honor and can show that your DC is at a certain level of math development. DS' pre-algebra teacher brought up SET at the beginning of the year as something that he can try. DS will probably take the SAT at some point in the next year or two simply because $50 and one morning is not that big of an investment.
You may consider Davidson's DYS program. Davidson provides free consulting services and will even communicate with the school to share the research to assist your advocacy efforts. I do find that ultimately you have to do your own advocacy.
