The student has spent three lessons on the opening page. Every run-through stops in roughly the same place. You could give it another week, but it's worth asking whether the piece is doing the job you picked it for.

A stretch piece should leave the student something they can work on between lessons. If they can't get started without you, you may need to change the assignment.

Find out where it breaks

Choose a short section and take away one difficulty. Slow it down. Separate the hands at the piano. Try the rhythm on one note, or isolate the shift on a string instrument. Let the student show you what they can already do.

If most of the piece is comfortable and one pattern causes trouble, that pattern might make a useful week's work. If nearly every measure brings a new fingering, rhythm, and range problem, a slower metronome setting may not be enough.

Ask what happened at home, too. “I kept trying from the beginning” tells you something different from “I couldn't figure out the first rhythm.”

Keep the part they care about

Maybe they chose this piece because they love the melody. Try teaching that melody by itself, finding a suitable arrangement, or choosing a shorter section with a sensible stopping point.

Explain what you're changing. “Let's get this theme sounding good, then come back to the bigger version when the shifts are more comfortable” gives the change a reason. Quietly replacing the piece without discussing it can feel like giving up on them.

You can keep the original as a longer-term goal. Give the student other music they can finish along the way.

Set a short trial

If you're unsure, agree on a small assignment and hear it at the next lesson. Demonstrate the practice steps, then ask the student to try them while you listen. Write down what a successful attempt should sound like.

Decide what you'll review: perhaps a two-measure connection at a comfortable tempo. If that connection is still inaccessible, look again at the method and the piece instead of extending the deadline indefinitely.

There is plenty of music worth playing. A piece that lets the student hear progress this month may be a better choice than one that keeps reminding them how much they can't do yet.

For help planning the smaller assignment, see Why “Practice More” Is Useless Advice.