There are at least 350 heads, past and present, included between the book's prestigious red covers. Admittance to the ranks of the privileged is for life, and defunct entries are enshrined in its sister volume, Who Was Who?
A spokesperson for Who's Who? says: "Any school that's doing well is considered. We compare league tables over a number of years. Because people stay in until they die, we don't want to invite someone whose school shoots up because of a change in statistics."
Mr McGowan would certainly have sprung to attention as secretary of the Scottish Executive's task force on school discipline. But is this enough?
The only other new Scottish entries for 2004 are, not unexpectedly, Graham Donaldson, HM senior chief inspector of education, and, more surprisingly, Gordon Woods, the warden of Glenalmond College in Perthshire.
Mr McGowan commented: "I have no idea why I have been included and it has come as much of a surprise to me as to everyone else. It may have something to do with the discipline task group or the fact that Banchory does well. I just don't know."
Who's Who? confirms that sitting on government committees is a consideration for inclusion. So also is publication of large numbers of papers, or schools having several famous alumni.
Primary heads, though, are deemed "inappropriate" for inclusion, unless they can boast other achievements as well.
Robert Jennings, head of Slemish college, in Northern Ireland, attributes his selection to having been named school leader of the year in the 2002 Teaching Awards south of the border.
He added: "I don't consider myself to have arrived socially. Still, I'm hoping a rich American might see the entry and decide to buy us a new sports hall."