I do it exactly the other way: put them on an empty road with a slight uphill.
With the parking brake on, let them practice getting a feel for when the clutch "bites". When it does, put the parking brake down and the car remains stationary.
Do that a few times (10m, or less) and the learner develops an intuition all by themselves for how the clutch pedal works (there's some travel until it "bites", the expected type of progression of the pedal, etc).
Can't teach that when they learn to use it like a button (which is what happens when they learn to change with the car in motion).
This is how I taught myself how after having multiple people tell me things like "it's just a continuous motion you do with both legs", "you just let the other pedal out while you give it gas", etc. Driving a manual seems to be one of those things that few people seem to be good at teaching because they forget how frustrating it can be to learn.
Instead what you want to do, what most people do subconsciously is let the clutch out partially until it is allowing the engine to apply some of its available torque but not all, and then pause there until the car’s speed roughly matches the engine speed, at which point the clutch will stop slipping even though you still have the pedal partially depressed, after which you should be able to rapidly raise your foot from the clutch and feel no acceleration or deceleration. For an experienced driver that pause is less than like half a second from standstill. Also technically the point at which you want to pause the clutch let out depends on a whole bunch of things like how quickly you want to pull off, how much torque the engine can provide and whether you’re on a hill etc, but we just do this intuitively with experience.
This is like a super over-complicated way to think about it and I would never try to teach a learner driver by first explaining this lol but the point is, you find the engagement point and hold there for a while and then release when the car is moving. This is what we all do but it helps to understand why we do it so we don’t explain things wrong.
I feel like people also don’t get what applying more throttle does while the clutch is slipping. All it does is raise the engine rpm, it will apply absolutely no more torque (and therefore acceleration) no matter how much you press down the throttle. While the clutch is slipping the clutch pedal controls your torque and therefore acceleration. You need some throttle though to give you some room for error and some minimum torque to work with.
But you’re totally right. You can pull away quickly by letting your rpm build up and choosing an aggressive clutch position while applying enough throttle to keep the rpm constant, alternatively in most cars you can pull away on a fairly steep hill with no throttle if you just barely let the clutch engage and hold it at that point until the car is moving steadily
Talk through the next bit first: Hold engine at 1.5k rpm. Ease off clutch just enough to start engaging and rolling forwards. Back on the clutch then gently break to a stop. Repeat until confident.
Etc. etc. The whole time the learner is in control of the car and they learn the basics without having to worry about steering.
Meanwhile some gas cars will stall without accelerator input at straight road.
Cars spend no time at .5 mph but plenty at 60. Tractors spend almost no time above 15 and tons of time at .25mph. tractors will pull your house over. Cars won't.
You can pop the clutch in idle in 6th in a tractor and it'll likely start