Here’s a thing;
Suppose the brain is like a battery, that runs out of energy when it is used;
When your student is playing a scale, especially if it is a new one, (and I’m talking piano here because that’s what I mainly teach), have you noticed that they may make it to the top, and even halfway back down again, but nearly always collapse, note-wise or finger-wise in the section.
Take a beginner playing a left-hand one-octave scale; up they go; 5 4 3 2 1 3 2 1 and down they come 1 2 3 4 5 “oh, I’ve run out of fingers”
Or right-hand D major; D E F# G A B C# D and back; C# B A G F E D – what happened to F~ on the way back?”
Hands together, two octaves – how often do they end up with an extra finger on the final note? Or missing a few sharps/flats towards the end?
I explain it to the students that they have used 70% of their “brain battery” getting to the top (which is the easier part) and have only 30% of their battery life to get down to the bottom (the harder part). So, if you were to start at the top, you would use 70% of your brain battery to get to the bottom (harder part) and 30% is probably enough to make it to the top.
Once I have taught a scale and the students know what they should be doing (even if they can’t do it) I always switch to “upside down” scales for a week so that they play the downward run while their brain is still functional, in order to consolidate RIGHT notes and fingerings instead of WRONG ones.
This seems to work, and if nothing else adds some variety!