What might be more effective than discussing LOGs, if you are not sure they are getting the point, is to gently note that the infrequency of such scores. Your children have scores in the 1 in 10,000 frequency, with VCIs perhaps closer to 1 in 20,000. A teacher with 30 kids a year would see such a child once every 300 years, 600 years or so...
ETA: Specific data, according to
http://www.iqcomparisonsite.com/iqtable.aspx, is that an IQ of 158 is at the 99.9944812644 percentile, representing about 1 in 18,120
Totally agree that this kind of perspective is important. Most teachers are familiar with "gifted" kids and pushy parents, but not HG+ kids. And when you look at the numbers, you can't really blame them for the lack of familiarity.
In my experience the most effective means of explaining the rarity of HG+ kids has been to throw out ratios for the general population AND give stats relating to the frequency one could expect to have kids like this in the course of a career (as stated above).... BUT I'd be very careful about wording. Trying to explain kids to a teacher is a bit like trying to explain juries to a trial lawyer. You might have some good points, but it's easy to come across as arrogant and condescending.
Better to print out supporting statistics and say something like, "
It's our understanding that if a teacher has 30 kids in his/her class every year, she/he would only see a kid at this IQ level or above every ___ years."
