We try to balance short lessons with longer ones in the highschool years. The rotating schedule is helpful for offering variety, but they do need to know that there are times when studies/work require long stretches of focus and determination.
Favorites: Life Purpose Planning Notebook, IEW’s Advanced Communications Course, and the Bluedorn’s Logic Books and DVD.
For those that aren’t yet at the highschool level, truly, the best friend you have is a timer. Use it to help them build focus and attention during the early and middle years. Each year, adding more time, helps them build up stamina. Learning outlining and note taking skills is super helpful!
Another suggestion is at least a minimal amount of root word studies.