Bartok was the national director of piano pedagogy for Hungary. to my taste, having a restart to my playing about six months ago relying on elementary pieces, the compositions he wrote for children are far more interesting musically and rhythmically than most other kids' stuff. your husband as drummer might appreciate BB more than most students, as BB focused on the myriad of percussive qualities in the instrument and his kids pieces focus quite a bit on developing touch, learning all the ways to control and vary the hammer strikes on the strings. many of his kids pieces are based on folk and dance tunes, coming from his ethnomusicology work throughout the Balkans. (quite a bit from one culture the german fascisti tried to completely annihilate from existence thirty years later). it's also easy to create a progressive course from bartok's works ; the kids stuff start at his 'first term at the piano' but get much more interesting and difficult going from there. the non kids stuff would start at the first three volumes of Mikrokosmos, designed to be progressive with vol.3-4 (there are six in all) breaching the line between beginner and low intermediate.
for my spouse's beginning studies, she has Bartok's first term at the piano and excerpts from Bach's notebook for Anna Magdalena, but she loves bach.