That's very interesting. I must admit, I haven't considered the importance of channelling sexual energy for the purpose of achieving a higher spiritual fulfilment but I can understand why it might be something worth learning and "training" for? Even on a superficial level, if the practices yield good relationship bonding and good physical health, then from what I can gauge, there isn't anything negative in trying.

There are some sayings in Chinese such as one drop of sperm is equal to ten drops of blood. And I guess this might have something to do with the idea of transmuting Jing into Qi. From my point of view, I think treating Jing as a scarce "resource" is one way of looking at it. Although it is true that unlike women, sperm can be produced throughout the life of a man, irresponsible use of that is like taking away the life energy which could have been channelled for use in much more "productive" ways during the finite time a man has to use his energy to make his life fulfilling.

To answer your question about what "proper sex education" might entail..

I probably wouldn't introduce them to seemingly advanced topics such as sexual alchemy because clearly there are grounds not covered at this point.

I think that sex education is something that isn't just a course that can be delivered in a small number of sessions at a specific age and then considered complete. For instance, what you mentioned would be a completely valid topic to be taught, albeit some time later when the child reaches or approaches that emotional tier of reasoning.

Thus, I think sex education should be delivered throughout adolescence, and support the transition to adulthood. The material should also be at a level that is relevant to their physical and emotional development. For instance, puberty should be taught before the onset of it, and sexual activity around the age children start to desire it.

The earliest delivery of sexual education should start with the anatomy of the different genders, and how they change going into adulthood. Items such as puberty should be taught so that dialogue on this matter between parent and child would be natural. (Things like periods, breast development etc.)

At this stage, I also think it's fine to teach how a baby is conceived and born. So, this would include intercourse and how sperm fertilises the egg. But this by no means advocates nor promotes things like sexual activity. This stage I feel is about understanding physical development and reproduction as a phenomena.

Throughout the teenage years, I feel more emphasis should be put on the emotional side of sex as well as relationships. This is of course in addition to more detailed coverage on different kinds of sex, and sexual orientations. Since in the early teenage years, some adolescents may even begin their sexual activity and so proper teaching on the various methods of contraception should be delivered. At this point, contraception ties in nicely with teaching about relationship dynamics, the emotions that might be felt, the responsibilities each individual has not only for their own sexual development, but also the people they engage with. Knowing the consequences of their actions.

With sexual activity there is also the importance of understanding how to be sexually healthy, in tandem with education contraception, things like sexually transmitted diseases and personal hygiene should be taught. Not only what the diseases are, and what is considered hygiene, but details on how to deal with issues arising from these two issues. Cancers, lumps and bumps should also be taught, how to identify, and what to do if you think you have it.

Perhaps some material relating to the broader purpose of sex outside of reproduction. Of course, they will have by now been taught it's purpose for reproduction, but may not have thought about the other reasons people choose to engage in various kinds of sexual activity. So, at this point it would be appropriate to emphasise the importance of respect. How not to feel pressured, or pressure people into engaging in activities they don't feel comfortable with.

As physical aspects of sexual education are covered in varying degrees of detail up to this stage, it's important to not leave out discussions on feelings and other aspects of relationships such as marriage, raising children, having a family etc. Different kinds of sexual orientations can also be discussed here, for instance Bisexuality and Homosexuality.

I guess after these grounds are covered, other topics I would expect taught in high school or even college would be things similar to sexual alchemy as you mentioned but also other contentious topics such as promiscuity, polyamory vs monogamy, ethnic and cultural differences in attitudes towards sex, relationships etc.