ShiroKuro Did you come into this approach on your own, organically, or did you learn about it?
I ask because I'm reading Dr G's book, and what you described is exactly what she recommends in terms of goal setting for practice sessions.
I'm happy to answer that. The story starts 2006/7 - three years in from lessons on a new instrument, first time ever in lessons - I was in a mess. Things had gone way too fast (3 grades, one year), plus a poorish first instrument ruining technique, as much as I learned any. By then I needed major remediation and relearning just for physical playing. I'd started brilliantly: it had all collapsed. I started hunting for alternatives, first for this other instrument.
The first starts there: I got told by someone to practise first "like vanilla pudding" and add things like dynamics later. Another time I'd gone in circles with a piece for 2 months - one day turned my back on the piece: focused on "string crossings" (violin) for the whole week, and coming to the next lesson, the piece I'd not touched all week was suddenly much better. That impressed me. Then for a given piece I always got stuck on "bar 14" - literally stuck, my glued fingers couldn't raise. One day I decided to work only on "bar 14" - find out how to "unglue" my fingers - got smooth motion; practised bar 13 into 14 and on into 15. Then I made several copies of the score, and used coloured markers. Found all occasions that were like "bar 14" (modulations of the same thing), circled them -- found the 2nd-hardest thing - the 3rd-hardest thing. I practised these in isolation and felt guilty the whole time, that I had done a "sacrilege" to music by chopping it up. 😃 A few years later I discovered "that's what professionals do".
There was a stint for a period with a teacher informally back then and re: the physical remediation part, who vehemently hammered in the idea of short practice sessions - very opposed to the idea of long hours of repetition and similar; mindfulness, awareness of what you're doing. Also the fact that when we think we're still focusing, we might in fact have disengaged minds. Also, that true engagement, esp. for new things, can't be held on for long.
I also did research at the time. I learned that in CAT scans, if you do a thing that is totally unfamiliar (learning to read music will be unfamiliar - improving your music reading abilities along existing pathways won't be) then your entire brain lights up. Once familiar, there's a designated spot in the brain, only that part fires, so it's much less fatiguing.
Everything with that instrument and lessons stopped the end of 2007, and I also got a piano (DP) again after 3 decades. I had learned self-taught as a child so essentially was in the same situation of needing to remediate and relearn. My "reading music" from that time was weird and also needed redoing. I sought out the question of learning music, student-teacher work, practice etc. on PW which I joined. Met a teacher for whom 'how to practice' was a priority - some of what he was teaching beginners were quite like the "sacrilegious" things I had invented. It was a synergy of what I'd developed by then, and some new things, and explorations. I was also alert for these kinds of things once being aware of them. It's a fascination.
Jaak Sikk for example, when he started his program that was (still is?) available on-line. I'm working a fair bit with Woroniki's material these days - you have to know how to work with it or it might be overwhelming and confusing.
What Molly Gebrian presents is a) old hat to me so far, b) very much needed for anyone who is out of the loop about these things. Had I known about them back when I started those first lessons, some things would have been different. I would have also had to know to insist on going slower, rather than just 'feeling uneasy' at the speed but doing it anyway.