It seems your first paragraph outlines a solution for the second paragraph. First spend some time teaching students using a method that works well for motivated learners and poorly for unmotivated learners. Then give a placement test measuring how much they learned. Put the people who did well in the placement test into a group that teaches motivated students, and the people who did poorly into a group that teaches unmotivated students.
It seems your first paragraph outlines a solution for the second paragraph. First spend some time teaching students using a method that works well for motivated learners and poorly for unmotivated learners. Then give a placement test measuring how much they learned. Put the people who did well in the placement test into a group that teaches motivated students, and the people who did poorly into a group that teaches unmotivated students.