First off I'm no teacher neither have I studied music. I have played the oboe for 15 years now and play in multiple amateur orchestras.
Now I have encountered situations where I'm asked to lead a practice session of the oboes of a youth orchestra which to me is a lot of fun. I really enjoy helping out and teaching them a thing or two. Also there usually is just one or maybe two oboes in those orchestras so I can really focus on them individually.
Now when practicing hard passages with a student I'm sometimes at a loss. I try to tell them how I would approach it and play along with them so they can hear how it should sound and if they are off somehow. I try to let them play the passage very slowly, even note after note if the fingerings are hard. Then I let them play it faster until we reach the right tempo but at that point I have often already lost them.
Since I only have so much time and there are a couple of other pieces that I should go through with them I eventually move on and tell them to practice that part on their own later, but I feel as if they didn't get any further during the session.
It isn't my job to have them play it all perfectly after we're done and I know that but it feels frustrating when you see that they don't make any progress. I don't want to tell them to leave out a harder passage even though I can see that they probably won't be able to play it right by the time of the concert because only by practicing they will get better.
So in the end I'm looking for different approaches for children to learn hard pieces since my methods won't necessarily work. I thought of introducing some kind of reward system if they play it right a couple of times. Or should I maybe not even focus too hard on certain passages but rather try to help them developp a better sound?