Our children play a variety of instruments, we developed an App where you could pick out sections of music and slow that part down. This was a huge help to break down tricky parts and slowly build up speed.
The App is free so the best thing is to download it and see how it works, a running App is worth a thousand words.
Other Apps were frustrating because you had to pay, the speed steps were too large, you lost your loops when you switched song or loop, the controls were hard to use, it was hard to get the music into the App.
We solved all of those problems with a clean circular interface, save as many loops as you like, no need to register, all functionality free. The only thing you need to pay for is if you want to turn off the advertising.
We bundled dozens of scales into the App. You can slow them down like the speed trainer, but it's also useful to play along at full speed and listen for any mistakes.
Before this App our children used stacks of cue cards, and had to judge for themselves if their scales were correct. Practice makes permanent and a few times they had learned the scales incorrectly
We are adding more scales all the time, so reach out if you want to request one.