It just so happens that Mozart’s Variation 3 of his Sonata in A Major, K. 331, presents the challenge of playing parallel octaves in LEGATO (smooth and connected) And to make the task even more complex, the composer uses the A minor tonality, with F# and G# inserted into the passage fleshing out the MELODIC form. It can become a slippery slope in any case, no matter what key is assigned to a passage like this.
Taking these snatches from the piano literature serves a double purpose. It builds technique as it expands repertoire.
In the attached video I demonstrate ways to practice legato octaves in a step-wise manner, emphasizing the need for a good, facile fingering. In addition, a supple wrist and roll of the arm also helps a student navigate the tricky musical terrain.
Behind tempo practice is always recommended, with a deep physical, and ear-attentive connection to notes and phrases. In this case the octaves have to play out in curves, like the preceding line, which meanders along as a singular spun melody. One can consider the octaves to be a variant of this opening phrase.
Play through without repeats (altered fingering for smaller hands)
Instead of starting 5, 4, 3 on upper part of the octave, I switched to 5, 5, 4–and followed when feasible with alternating 5 and 4–
At the end on E F# G# A, I used 5, 4, 5, 5
“I use 1 and 5 throughout except near the end where one goes from white to
black notes. The pedal changes on the 1st and 5th beats throughout.”
“Oh, those legato octaves! Not only in Mozart but also in many other pieces. Of course, the size matters! Big hands play octaves easier, and it would be funny to deny it. For example, the fingering that you suggest is really good…. for big hands. In a slow tempo I myself could use but in a faster tempo that would be more than challenging. However, even a pianist with small hands could shape the passage well if he has enough sound control (plus just a bit of pedal, carefully!). Many things that we do playing piano are illusions, and that is a whole interesting subject. So it is possible, in my opinion, to create an illusion of legato in octaves even with small hands.”
Suggested Lowering the wrist through the octaves, and this was very observant and helpful.