Yes, "set in motion" does have a unique function compared to other synonyms like "trigger" or "propel." While all three convey the idea of initiating or starting something, "set in motion" emphasizes the act of beginning a process or action with a sense of deliberate action or intention. It implies that something has been put into action with a purpose or intention behind it. In your example sentence, "set in motion" suggests that the introduction of calculators into classrooms was not merely a passive event but rather an intentional action that initiated a broader change in mathematics education. It implies that there was a deliberate decision or effort to introduce calculators, which then led to significant changes in the educational landscape. Using a phrasal verb like "set in motion" can indeed add depth and nuance to your writing by conveying a specific meaning or emphasizing the intention behind an action. It can sometimes capture the subtleties of a situation more effectively than a single verb. In your sentence, "set in motion" effectively communicates the deliberate and purposeful nature of introducing calculators into classrooms and its subsequent impact on mathematics education.

I believe "set in motion," "trigger," and "propel" carry shades of meaning based on their original, literal usage. A gun has a "trigger," and is "triggered." It refers to a small force that triggers a single, loud, violent explosion. It also has a characteristic of suddenness. You gradually increase the force on the trigger and suddenly the gun fires. A machine is "set in motion" by starting it. It carries a feeling of some mechanical complexity. The motion is steady. "Propel" makes me think of a ship and its oars, or its propellor, or an airplane propellor. It refers to something that is already in motion. It makes me think of the continuing source of energy needed to maintain that motion.

You can almost use "trigger", but not "propel". "Propel" is what rocket fuel does for a rocket. It doesn't just start the rocket; it keeps the rocket going after it has started. "Trigger" and "set in motion" only speak of the starting. The difference between "trigger" and "set in motion" is that "trigger" supplies no force whereas "set in motion" does Possible synonyms (depending on context) for "set in motion" are "begin", "initiate", "cause", "start", "precipitate", "engender", "spark", "occasion". Here are some examples: "The student's truancy precipitated a descent into a pattern of ever increasing anti-social behavior." "Mary is a great dancer. Her arrival at the party occasioned a dancing spree that lasted past midnight." "Having a math teacher who could really explain things well sparked an interest in little Billy that lasted his whole life through." "The charity's mission is to engender self-reliance among people whose lives seem without hope." "The teacher began the course with a lecture on the usefulness of learning English."

'To set in motion' implies some kind of causal relationship, so it generally means 'to cause' or 'to result in.' 'Trigger' is also similar: something causes or triggers some resulting action to occur. The example sentence as written seems good/natural. 'Propel' can also be used, but it suggests more of a continuous effect, whereas 'set in motion' implies a more spontaneous resulting process, i.e. something like gravity where the action simply frees up the system to find a new equilibrium point whereas 'propel' could be thought of as a continuous action, more as a rocket, or something like that.