It's really not at all a pivitol a moment in the novel. I'm sure it was not in any of the screenplays (although plenty of weird Gene stuff is).
It is referred to in Kirk's foreword to the novel where he explains his name. (Sorry, JJ, his grandpa's name is not Tiberius.) "I received James because it was both the name of my father’s beloved brother as well as that of my mother’s first love instructor."
(I never realized that SAM is named after his grandfather.)
OK, we all love to bag on Gene's obsession with... To just say "sex" doesn't seem to do the man's demons justice. I mean TWICE in his Motion Picture Novel he has Kirk having to deal with the unwanted excitement of the Kirk Unit in front of his crew. (Both times because of Ilia's pheromones.) Wait. No, there's another moment when he sees the hologram of Lori, his lover and we get to hear about his physical reaction. Good grief, Gene was almost SIXTY! Grow up a bit, sir.
Anyway, it's actually a decently sci-fi "advancement of the species" kind of idea that humans would become comfortable enough with sex that it would be actually taught like you teach driving or manners. Maybe I'm reading too much into it since he calls it a "love instructor" rather than simply sex ed and the implication is that Kirk's mom had an emotional attachment. It also sounds like a really Roddenberry idea. The fact that it would be totally understandable to name a child after someone in this role normalizes it even further. Very Gene.
Your mileage may vary on if you might think this is a good or an ill. Suffice it to say that we're clearly not even close to that point yet even if one accepts it as a good idea. I don't but then I don't believe in Roddenberry's perfectible humanity either.
(Happy 45th birthday, TMP!)