The idea of sound being associated with vibration is evidently being developed, but this student considered that sound could only travel through air and so had to emerge from the drum through the holes. In the second figure, the student has been investigating a string telephone. Both of these examples indicate to the teacher the kinds of further experience and discussion that will help these students' understanding of ideas relating to sound. Of course, the teacher will be gathering similar evidence from other students in the class and will be able to find out to what extent these ideas are generally held. This information will help to decide what issues should be addressed, and whether it applies to all or just some of the students.
Students are ultimately responsible for their own learning.
In making the request, the teacher must ask for the thinking behind the work. The two figures would have been much less informative had the teacher simply asked the students to draw the instruments. The advantage for the teacher in making this request was matched by the advantage for the students, who would see a purpose for their work, as a contribution to sharing ideas. Similarly, the student who wrote the passage quoted above would see that the point of the work was improving the investigation, and not just a matter of writing something as a routine. As the teacher studies the students' work, all the information gathered is potentially helpful, not just the mistakes children make.