IMO this would be helpful when practicing completed lessons as there won't be a hassle of selecting it.
Are your really using version 16.12.0? What you are wishing is one of the few new features in this version. Pressing [Space] should take you to back to training, either on the next or current lesson depending on your success.
16.12.1 to be exact. Focus definitely gets set on the Next Lesson button after a failed attempt.
Git commit b2fdf0f9382b93d47e06fa8fa3dc417e73913626 by Sebastian Gottfried. Committed on 23/01/2017 at 09:58. Pushed by gottfried into branch 'master'. Score Screen: Revise Focus Policy Always set focus to the button "Repeat Lesson" if the user has failed the lesson he just has trained on, even if he has unlocked the next lesson in a previous training session. This makes recapping a previous lesson easier. FIXED-IN: 17.4.0 M +1 -1 src/qml/ScoreScreen.qml https://commits.kde.org/ktouch/b2fdf0f9382b93d47e06fa8fa3dc417e73913626