I was educated in Asia before college and we know how important it is to have good math basis. The addition and subtraction are mainly done by mind calculation not on the calculator no matter how big the number is.
This text book or math teaching system is well designed for English speakers. At the beginning, I like it start from counting numbers and connecting them from symbols to letters. The work book makes exercises fun, my son can concentrate on the book for almost one hour.
Overall, it’s a good math learning system.