From the team:
"In selecting examples for each exercise, certain considerations have been taken, like not allowing too many examples to follow a single vocal pattern. This is to avoid students guessing the pronunciation of an example based on the last one, when they are supposed to work out each example separately.
We have also tried to make sure that not a single example contains any elements that they have not yet covered. For example, no examples will have fatḥahs until fatḥah has been formerly introduced. Likewise, examples containing ikhfā have been left out until the student has learned about ikhfā, and so on.
We then arranged the examples in each exercise so they progress from the easiest to the most difficult, taking into consideration the number of letters or words in the examples as well as the weight and difficulty of the letters."