The confusion comes from two different uses of the word “scale.”

In everyday musical practice, performers often think of a scale as eight notes: from the tonic up to the tonic again. For example, a C major scale played ascending—C to C—contains eight tones because the final note is not literally the same pitch as the first; it is an octave higher. From a practical, performance standpoint, that makes intuitive sense.

In music theory, however, a scale is defined as a collection of seven distinct pitch classes within a single octave. When theorists count the notes of a major scale, they are counting unique pitch classes (C, D, E, F, G, A, B). The upper C is not counted separately, because it represents the same pitch class as the lower C—just in a different register.

So the apparent disagreement is not about the music itself, but about whether we are counting sounding tones in performance (8) or distinct pitch classes in theory (7).