It depends. I mean, different schools, different teachers, different approaches. In my school we combined intervals, scales and arpeggios. For instance, in the first year we learned basic scales (natural major, harmonic and melodic minor). We learned their intervalic structure, main chords (T,S,D) and we sung all that stuff. So, theory and solfeggio were always complementing each other. It’s not like we learned scales and intervals separately. More like ‘Okay kids, major scale includes 3 major thirds and 4 minor thirds. Let’s sing them. Do-mi, re-fa,mi-sol…’. Ascending/descending, starting from a random note etc. The same with chords: leraning intervalic structure and singing arpeggios of main form, 6 chord, 64 chord.
btw learning intervals in scales helps to understand why one and the same interval could be called minor 3rd in one case and augmented 2nd in other.