Assuming that it can be taught. It's possible that the key components that link conscientiousness to academic success are prefrontal/ventral tegmental stuff such as different reward mechanisms (motivation, willpower) and differences in executive function (attention and inhibitory control), and we don't know to what extent teaching can modify that. Executive function, at least, seems difficult to alter via training.
Plus, we'd have to separate out the components of conscientiousness though - it's possible that conscientiousness is not entirely positive. Conscientiousness has a rather controversial relationship with fluid intelligence and creativity, (as usual, most stereotypes carry at least some distorted truth) though it's too soon to make definitive statements.
I do mostly agree with you - these are just rather important qualifiers.
When we talk about training executive function through principles such as Dual 'n' Back we are talking about relatively little time investment.
A child spends years in school much longer than your average psychology study runs.
The soon-to-be-resigning Dominic Cummings, advisor to the Education Secretary of the Coalition government, has released a 250-page manifesto describing the problems of the British educational establishment ("the blob" in Whitehall parlance) and offering solutions. I post this here because both his analysis and recommendations are likely to be interesting to LW, in particular an increased emphasis on STEM, broader knowledge of the limits of human reasoning and how they relate to managing complex systems, an appreciation for "agenty"-ness in organizational leadership, whole-brain emulation, intelligence enhancement, recursive self-improving AGI, analysis of human interactions on a firm evolutionary-psychological basis, and a rejection of fashionable pseudoscientific theories of psychology and society. Relevant extracts: