The philosophy of Saxon is that learning need not be difficult, but it does take time. As a result, the publisher takes an "incremental" approach, which means they introduce concepts in small pieces and then continually review that concept as they add more pieces. Topics are never dropped; instead, they are gradually increased in complexity, allowing them to become second nature.
In these four levels, the format of the series completely changes, and this is where we begin to strongly recommend Saxon. In the kits, there are again three pieces, but this time they are the softcover student textbook, solution manual, and the tests and worksheets book. The textbook offers all of the teaching material, including daily warm-ups, the introductory material for new concepts, example problems, practice sets, and daily work. In the current editions, all four of these levels include 120 normal lessons and 12 "Investigations" (one after every ten lessons). The lessons are fairly readable, and the number of problems in the daily work is manageable, a few practice problems and usually between 25-30 questions in the problem set per day. The test and worksheet book offers manipulative copy masters, multiple copies of drill sheets to go along with the lessons, and tests to be offered regularly. The solutions manual is a step-by-step answer key for every problem in the book (and for the tests).
We really do think these books are one of the best choices around for grades 4-8. Granted, we've heard complaints about them, but (in general) find those complaints come from unimaginative teachers. We remain convinced that the books will offer a solid preparation for the higher levels of math and that they can be adapted for use by most families. There are a variety of ways to do this, and we would be happy to talk to you about some of the possibilities. If you would like additional help incorporating the [seemingly disorganized] concepts into a unified whole, take a look at the DIVE CD-ROMs.
The numbers "5/4" mean the book is meant for an "average" fifth grader or a "bright" fourth grader. But, if possible, we recommend using them even younger. It won't work for everyone, but we think being done with 8/7 by the end of sixth or at most seventh grade is a good goal.