The fourth string of the ukulele (the string closest to your face as you play) is typically tuned an octave higher than might otherwise be expected (hence the familiar "my dog has fleas" tuning, also referred to as re-entrant tuning). In the classroom context, however, the authors strongly recommend the use of "low fourth string" tuning (known as “linear” or "sequential" tuning).

In linear tuning, the fourth string is replaced with a thicker string and tuned down an octave (a reversible procedure). This extends the melodic range of the ukulele by five notes. While much of the material in the Ukulele in the Classroom series is playable in either linear or re-entrant tuning, accompaniment parts – which add a great deal to the learning experience – usually extend into the low fourth string range. Furthermore, linear tuning helps to clarify the structure of scales and chords.

It should be noted that re-entrant tuning has unique qualities that students should be encouraged to explore, particularly once they have mastered Book 3 skills and repertoire. At the outset, however, a ukulele in linear tuning is a superior tool with which to explore the fundamentals of music. For this reason, Ukulele in the Classroom is written, first and foremost, for ukuleles tuned with a low fourth string.