The German word "Stellschraube" means, in its technical sense (according to dict.cc):
However, in a metaphorical sense, it can also mean a "leverage point" to adjust something non-technical. For example, motivation might be a "Stellschraube" for teachers to create a fruitful learning atmosphere.
Is there an English word having a similar meaning?
You've used the word, leverage.
Car privileges can be used as leverage to get your teen to take his or her studies seriously.
Here I think the metaphor involves a torture device:
If your teen is not taking his or her studies seriously, you can tighten the screw and deny them car privileges.
“Leverage” does work, but it feels somewhat antagonistic for the purposes of your example: “A teacher may leverage motivation to create a fruitful environment,” or “A teacher uses motivation as leverage to create a fruitful learning environment.” The former sentence is OK, but the second implies that she is using motivation as leverage AGAINST something or someone. In this sense, the literal and metaphorical meanings of “leverage” are inherently oppositional: weight at one side is moved only by greater weight at another side acting against it. This we typically use “leverage” to induce someone to do something we want, frequently at their expense.
I feel like your example is somewhat less antagonistic, and you could just say motivation is a “tool” for teachers to create a fruitful environment. A setscrew is a class of tool, so the metaphor is preserved, albeit tenuously.
“Leverage” is probably truer to the German literal translation, but I would shy away from using it where there is no conflict or opposition involved, as in your example.
