Incidentally, we are also using the expensive version currently at Grade 3.5x. The "Set" concept is formally introduced in Grade 3, but informally in the lower grades as "Counting in Groups". The titles of the concepts are somewhat overkill for the actual materials introduced in the lower grades. Our experience with the questions is that either you know how to work out the answers or you don't. There are essentially no tricky questions at all. So the progress is like a period of near 100 %, until the next unfamiliar concept; and then after mastery, another period of near 100 %, and so forth; in particular, since the program allows 2 attempts for each question, careless wrong answers are reduced to almost zero. We find that the learning process is more efficient to complement the program with some offline tutoring on the unfamiliar concepts. Overall, the breadth of the concepts introduced is richer than other sources that we have encountered.

Thanks Melissa and Chris for their effort and time in volunteering for the SSA.