Agreed. And double for Portia's comment that most people think they know what gifted means, but really don't have a clue about the kinds of giftedness that drive people to this board (heck, until DS came along, neither did I).
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
