"Over 0.3 per cent of children are born with some kind of chromosome disorder."

The numbers have actually been quantified, I am amazed.

"Most develop Downs Syndrome"

But Downs is not a sex chromosome disorder, so why mention it?  You don't mention Fragile X that does cause mental retardation, and this article is about sex chromosome aneuploidy.

"or obtain the wrong number of sex chromosomes and develop Turner's or Klinefelter's syndrome."

Whilst it is true that Turners is present at birth it is not true of Klinefelters syndrome.
Klinefelters syndrome only develops after the onset of puberty.

"Turner's syndrome only occurs in females"

That is not entirely true.  There are such people as Turner Mosaic Males.   And to be realistic, the missing chromosome can be a Y.   Most people just assume the missing chromosome was another X

"Girls with Turner's have arrested development and if no treatment is given do not enter puberty."

They are short in stature but mentally normal.  I think "arrested development" gives the wrong impression.  

"Klinefelter's syndrome affects males, who receive an extra X chromosome."

Or who can have ANY degree of additional X  genetic material, even just a mere repeat sequence of and X, on their one and only X.  XY males can develop Klinefelters syndrome, and I know a man with just this karyotype so, expand your knowledge!  

"Symptoms include concentration difficulties"

Utter rubbish.  See males and females with Kallmann syndrome and you won't find any such thing.  Hypogonadism is what Klinefelters syndrome is, and a primary cause.  Kallmann  syndrome is a  secondary cause, and evident prenatally yet no educational difficulty or memory difficulty is found.  

XXY and Klinefelters Syndrome are not the same things  

"poor motor skills"

Not related to hypogonadism'

"infertility."

One out of three, you can do better.