|XP is just a number|
Already a long thread but...
for some reason i always try to get motive behind things, and here's what i ascribe to the situation you describe, which not only seems to explain things but also gives a general instruction as to how the curve will continue later (everything's a curve, it's just that sometimes that curve is a straight line; damn mathematicians... ;-)
The teachers of current generations are different then the teachers of my generation. So i don't plan on starting from the beginning where some anomalies happen, but instead explain what i think the cycle is now that it has stablilized.
Note how at every step (3) only the basics are taught, because at any one slice of time the subjective term "basic" means different things, and people who are up on current practices will (more than likely) scoff at what is being taught in grade/junior/high/etc school...
So, in my opinion, the money is not going to waste, because in a few years when the next generation of teachers starts in, they'll start teaching higher concepts and levels. And those kids will be able to grasp more and more. This bumps the bar on what one "needs to know" to get through school (and thus survive -- for some definition of survive) but in the end it makes the whole of people slightly smarter over time (which to my mind is the point of education).
As to when is it too early to teach kids? That's child dependent. For some strange reason i have very early memories to before i was 3 years old, which is unusual, and my comphrension of material starts from that time onward. Some kids don't start remembering (and thus comprehending, that is to say, learning) until 4 or 5 years. IIRC the average is 3. As soon as the child is ready to start learning what they want to learn then by all means start teaching. Children are information sponges, but like all sponges they should not be squeezed. To forcibly teach something they don't want to learn will just dry out their thirst for knowledge...
Disclaimer: As always, the parents should have the final say on what a child does or does not learn during their formative years.
Anyway, those are my opinions, and two cents, take them for what you will...