So let's take your bug example... I know it was just a silly one, but let's go with it.
This is what I actually experience:
My child bursts out of school, full of beans, telling me excitedly about a load of bugs. Did I know about this bug, that bug? Etc etc.
At this point I'm already thinking, wow, they learn a lot, what even are all these bugs, did I used to know all this too?
Then maybe DC seems particularly excited about one of the bugs. "Mummy, they each have a different pattern, and they live in the desert and they burrow into the sand"
So then I say "Wow, really? Tell me more. Maybe we can find a video of one burrowing in the sand! What else do they do? Let's find out!"
In summary, I find that the school provides so much stimulation and broadens horizons, in ways I could never predict. My child is then free to follow up on anything they have found particularly interesting, outside of school. Obviously, at infant school age (heck, any school age, I'd say), broad exposure should be the priority. The desert bug isn't the thing - the spirit of curiosity and joy is.
I know you brought this example up in the context of teaching to a test. On the topic of testing, I'd add that testing is a core part of any teaching. I suppose you know that as a tutor? Any trained teacher knows that testing knowledge and understanding is an essential part of the learning process, else learners can slip through the cracks. It's not necessary for any teacher, parent or child to link that to extrinsic motivation, or develop personal hang-ups about it, lending it undue significance. It's a learning tool and no more.