We use Singapore Math and I would recommend it. We started it after finishing Miquon (also highly recommend) in 3rd grade for dd10. (I'll do the same for dd8 when she finished Miquon.) At first she was NOT happy to stop Miquon, so she disliked Singapore Math just because it wasn't Miquon. She got over that and we've liked it a lot since then.
I had been advised by other hs moms to start at Singapore 3A to get an introduction to the word problems and how they map them out.
We went through 3A and 3B fairly quickly getting acquainted with it and doing some review. DD10 is now in 5B. She mostly does the lessons on her own now and then does the workbook assignment that goes with them. She comes to me if she has a question or doesn't "get" something.
I do like the focus on word problems and the mental math. I'll admit that we don't do all of the mental math "extras". Sonlight sells this program in a kit of sorts. It comes with a teacher's guide (with answer keys), the Singapore text and workbooks, and the Key to... series. So far, we used some of the Key to Fractions and Key to Decimals. Dd10 said they were very helpful as review.
As for Standardized Testing...we also do that. In TX, I'm not required to do any testing, but I do it for ME. I've used the CAT5 (California Achievement Test) since dd 10 was in 1st or 2nd grade. I think the real value of the test is not seeing the numbers at the end, but actually seeing for myself which questions my girls have trouble with. Sometimes a low score can just mean we haven't covered that. For instance, in Miquon Math, they were introduced very early to multiplication, division, fractions, etc., but the subtraction that much of the test was geared toward at a certain level was in just around the corner for us. I didn't panic because I knew we would soon be getting to it. I reassured dd that it was ok that she didn't know all of the stuff on the test, that she knew tons more than they were testing her on. The same goes with social studies. We started with World History, whereas most schools begin with American History. My girls didn't know some of the things that the test was based on because of that. Again...no worries, because we were doing great with our World History and knew that Amer. Hist. was right around the corner.
I get my materials through Thurbers.net. I sign up for a specific week of testing (I do the same week every year). They send the materials, I administer the test, and then send everything back to them. They send the results several weeks later. This has worked well for me and I recommend doing the testing yourself for the best benefit.
Yikes, this is too long!! Sorry about that!!