You might be interested in this quote
There are three children in a million who are 'profoundly gifted'. Conventionally this means they have measured IQs of 180+. It is likely they will have spoken in sentences at 6-9 months, learned to read and spell by the age of 2 1/2, self-taught, and are ready for formal learning by the age of three. ...
By the age of 10, if allowed, they will have learned the whole of the National Curriculum and passed GCSEs and be ready for A levels. ... Within a year or so they will have passed A levels and be ready for University
Taken from the Introduction. Gifted & talented children with special educational needs. Diane Montgomery. 2003
and later in the Introduction
Hollingworth (1942) and Pickard (1976) found that with an IQ above 155 very few children were happy or could be maintained in ordinary classrooms ...
I suspect that the IQs mentioned refer to Stanford Binet L-M. For an idea of levels of IQ from more usually found tests a glance at the levels needed for Mensa membership is useful.
A top 2% mark in any of these frequently used tests below qualifies you for entry to Mensa. The minimum test mark to get into Mensa is:
* Cattell III B - 148
* Culture Fair - 132
* Ravens Advanced Matrices - 135
* Ravens Standard Matrices - 131
* Wechsler Scales - 132
At both the Infants and Primary school my DS attended/attends there are a group of children - 2 children from each class within each year group who have a "thinking outside the box" type session once a week. This can be a lifeline for some children who find the repetition within the ordinary classroom a challenge.
Hope this helps