The repertoire in the Suzuki method is designed in such a way that the child can progress from music that is very simple, to very demanding repertoire, always with a feeling of mastery. The student will take small incremental steps which lead to thorough confidence and mastery on the instrument. The job of a Suzuki teacher is to take the smallest task and break it down even further for a student. We need the student to feel confident and secure, not frustrated. The repertoire is arranged very well to accomplish this task, as generally speaking, each piece presents one new demand on the student, so the student is free to focus on the one new issue, as the previous issues are completely assimilated into their playing mechanism. It is a well researched pedagogy and is reaping benefits for thousands of children.
Parents are often unrealistic in their expectations of what can be accomplished in a given amount of time so it is crucial for them to understand the time-frame that teachers are operating under. Learning music takes years and years, not weeks, and the expectation of the child, parent, and teacher must take that into account.