We bought the following. There is a set of materials for each half-year; for example, there is a 2A HIG/TG, textbook, and workbook to cover the first half of second grade.
1. Home Instructor's Guide (HIG). This is similar to the Teacher's Guide (TG), but more focused on teaching a single student than an entire classroom at a time, and it's cheaper. It contains lessons, interspersed with enrichment activities. This or the TG should be all the guide you need.
2. Textbook. This contains enough teaching at the start of each section that we don't use the HIG as much as we expected, just checking it to make sure we're not missing out on something important. Each one is about 150 pages.
3. Workbook. This contains extra practice problems, and we initially never even cracked it open since our son tends to chafe at too much drill, and since Singapore revisits learned calculations and concepts often in review sections in the textbook. Upon looking at one recently, it isn't just drill-and-kill; the format is varied, and some of the problems are in puzzle-like formats.
3. Challenging Word Problems / Intensive Practice. Extra word problems, etc. We pick some problems from these.
If I had to pick one type of SM resource to skip for our son, since he picks things up fairly quickly and I have a head for teaching elementary math, it'd be the workbooks; after that, the teacher's guide.
We bought the Standards Edition (translate to: "California educational standards edition"), which is similar to the U.S. Edition but has earlier and more treatment of some subjects.
We ordered a few years' worth at a time from christianbook.com . We are non-religious but like this website, since it has good prices and excellent service. If you get your order over $100, shipping is free, and when I last shopped they had the lowest prices on the Standards Edition materials.
