But, excruciating as I'm sure it was, it probably takes a back seat to Knowledge for the Growing Boy by Sid G. Hedges, first published in 1941 and kindly made available by Ship of Fools for download in 2008.
There's a little background information also available.
You have to remember that, stilted though it is, it's still probably more than boys were officially being told until then. The Revd Chad Varah founded the Samaritans after a girl in his care killed herself ... because she was having her first period and didn't know what was happening. You can't fault the motivation to be helpful, and its advice on generally healthy living, treating the opposite sex as friends rather than sex objects etc. is valid in any time period.
His uses for discarded cotton reels, on the other hand (page 18) might raise eyebrows.
Yes, we have moved on from this time, but that time itself had moved on from what was before it. Boys were considered ready for some, but not all information ...
The "semen" is discharged from the "penis" into the passage in the female body behind that through which the urine is discharged.A particular bone of contention with Sid is that way too many boys apparently waste this "important fluid" deliberately. (Though in the absence of any females lying conveniently close to them it's hard to see why they would want to. [Yes, his all-important tip for making love is that the couple are lying close enough together for it to happen.]) Up with such Sid will not put, though he does concede that the habit, once acquired, may be difficult to give up. It's still doable, and without the slighest sense of irony he extols us in a little couplet:
"For the things that are easy have little regard,
But always be glad for the things that are hard."