IMHO the idea of school is to teach students how to learn. Knowing when a certain battle happened isn't important, understanding how to view the world through the lens of history is. Knowing how to study the historical background of a culture or society should be what the student learns.
Likewise, the goal of English class is not to memorize the parts of speech or memorize famous poems. Learning how to write prose, master communication with the written word, and coherently communicate their thoughts, loves, and desires upon paper, are the ideals towards which students should strive.
Essentially, why aren't good study skills explicitly taught and practiced?
What I've experienced through school is that whilst there is some implicit teaching of such skills, a lot of study skills are either found by students themselves through experimentation(random), or passed down from their parents. More often than not, these are attrocious for students that did not have enough parental involvement OR parents that don't know how to study efficiently either. My personal hypothesis is that these are affected by and also affect socioeconomic standing. Just like wealth, education also perpetuates through generations.
Personally, through highschool my aproach to studying involved cramming, keeping almost no note of due-dates and very messy planning of long term academic projects. In fact, anything that took more than 2 weeks of foresight would leave me scrambling to finish at last minute.
What's worse is that this did not occur to me to be a problem until well into 10th to 11th grade, which put a dent into my college prospects to say in the least.
Since then, I've been working on aquiring these skills on my own, playing around with things like holistic learning, spaced repetition, learning how to structure projects and aquiring organizational tools such as org-mode or even something as simple as using a calendar habitually. And it helps immensely.
And whilst now I'm starting to put these things into place, I keep asking myself: "Why was this not pointed out to me back in ,say, 6th grade?". General education is a great social equalizer, but the assumption that these neccesairy skills are simply passed down seems to go against that very idea. My personal opinion is that teaching these skills would have an incredible impact, since often intelligence is not the problem, but methodology is.
But the assessment doesn't have to only assess facts. The assessment can also include complex problems; it would however require that an answer be an absolute value. This teaching method would not be appropriate for all learning material. But it might be good for 70%. Even English has fundamental/structural "facts" that could be assessed this way.