much more than "knowing" that they can learn.

In my opinion, the first requirement for a "scientist" of any age is to have imagination.
Teach them to read, write and do arithmetic, then give them gifts of sci-fi and scientific books to read, encourage them to imagine things that might be, then do "prescribed experiments" to show what has been learned, then encourage them to imagine a "goal" that they may want to reach, then ask them to figure out how that goal might be reached, give them the means to experiment and test their assumptions, be instructive and supportive, never criticize a failed experiment, (remember Albert Michelson and Edward Morley) there is always something that is learned by doing things.

I guess that is what they mean by saying:

But too many classes focus on doing prescribed experiments. Missing in many schools are activities that emphasize scientific process: stating one's own theory, designing one's own experiment to test the theory, gathering data from the experiment, and using the data to confirm or revise the theory.