Do we learn to improve our working memory capacity without sitting WM tests? Do we learn to improve our working memory capacity without sitting WM tests?

Working memory capacity can be measured, but I wondered whether the only way to improve it is learning techniques for working memory tests (such as the digit span test)? I think I remember that working memory capacity is relatively stable in adulthood and reaches that level at a relatively young age in childhood. So I'm asking whether general education improves our WMC, not for supposed brain training techniques.
I'm not a psychologist so be cautious about drawing conclusions from what I say.
Education can teach us to use our working memory more effectively by:

Learning how to do better chunking (which sometimes comes at a cost of time and effort spent on recall and on creating the chunk, but this can be improved with practice).

Using our strongest domain(s) when appropriate, taking into account our capacity and &quot;chunking skills&quot; in each domain.

According to this answer:



The evidence for domain-specific modalities is largely based on the (lack of otherwise expected) interference between them.

This means that maybe you could spread your items-to-remember across different domains to use otherwise untapped capacity, and (based on information from the linked answer) the usage order of domains matters.
However, since some (if not all) of these methods come at a cost and require conscious effort, the advantages of remembering more this way are limited and not equivalent to increasing your actual working memory capacity.
Examples:
Remembering a number by the pattern it draws on a phone's unlock screen.
Remembering a shopping list by imagining a set of (memorable, ridiculous) images where each image includes 2 items, one of which is also included in the next image (1st image: items 1 and 2, 2nd image: items 2 and 3, and so on). Then you can recall the first image, and recall each next image by asking what other image included an item from the current image. This is a good example of how verbal/auditory memory isn't always the best choice for remembering a list, unless your visual memory is much worse.
Remembering a number by recognizing (mathematical or other) patterns in it, so you can reconstruct the number (or part of it) from these patterns.

While you didn't ask for &quot;brain training techniques&quot;, training is part of learning, if you want to become educated on how to use your working memory more effectively, you will need to practice the methods and see them in action, and they involve using skills that will improve with more practice.
For more information, read about methods of memory champions - people who manage to quickly memorize many things, such as card decks, long numbers and speeches. Their methods can be used by anyone, you don't have to be an exceptional person to be able to do impressive things with your memory, I tried it myself and was surprized at how well and how easily it worked for me.