If there is a training effect in increasing magical strength, and or improving concentration, keeping the rock transfigured works that way too, without being Transfiguration specific. Quirrel’s armies help too—would normal classroom activity exhaust magic that much?
Harry could try a controlled experiment over the Easter holiday if he thinks about it. With McGonagall’s permission, ask his classmates to keep a loop of cord transfigured into an unobtrusive platinum toe ring (or more than one) over the holiday when they’re not otherwise allowed to use magic. Then compare deltas in transfiguration scores on the next test between those who did & didn’t attempt it.
Is Harry getting letters back from his parents? He doesn’t yet seem to be thinking about measuring magical strength, but a tool to compare would permit some kind of scale—if it could use embodied magic in magic items as markers. That could argue for faster access to later year charms. Similarly of pre-electronic tech that may be useful, that his parents may remember. (Slide rules, Curta calcs, Microfiche & hand held readers, …)
Chapter 24: Machiavellian Intelligence Hypothesis: Act 2 … The line of reasoning continued: Atlantis had been an isolated civilization that had somehow brought into being the Source of Magic, and told it to serve only people with the Atlantean genetic marker, the blood of Atlantis.
And by similar logic: The words a wizard spoke, the wand movements, those weren’t complicated enough of themselves to build up the spell effects from scratch—not the way that the three billion base pairs of human DNA actually were complicated enough to build a human body from scratch, not the way that computer programs took up thousands of bytes of data.
So the words and wand movements were just triggers, levers pulled on some hidden and more complex machine. Buttons, not blueprints.
And just like a computer program wouldn’t compile if you made a single spelling error, the Source of Magic wouldn’t respond to you unless you cast your spells in exactly the right way.
The chain of logic was inexorable.
Under that hypothesis, accidental magic by wizarding children — otherwise without appreciable magic power, could be a Source of Magic initiated emergency “Help” spell.