Given:
Sample size = 24
Given that she wants to ask the students which of the 5 speakers they would most like to hear, let's select the group of students she should ask to get the most representative of the sample.
In this case, the best group will be selected randomly to prevent sampling bias.
Hence, from the list, the best group to select is:
4 students from each of grades 1 through 6 at the all school