For those familiar with singapore math: DS took the singapore math placement test for book 2A and scored a 72%. Should I have him do the next book or do the book for 2A. The website suggests to move to the next book when a child scores a 80%. Does anyone have any advise for me? Thanks!

I would look through his answers and see which topics he had trouble with, work on those and then move on to the next level when you feel like he has mastered them. Also , I would check the next book and see if the topics he missed are reviewed much already.

My ds is wrapping up 2a right now. To be honest I gave him only the 1a and 1b tests. I looked through the 2a book and knew to start him with this one. Looking at the 2b book, he will need many of the skills learned in 2a to be successful. That being said, I think my ds will breeze through 2b pretty quick. From a quick glance it may be easier then 2a if that makes any sense.

You can use curriculum compacting to make sure you don't skip anything he needs to learn, but skip what he knows already. An easy way to do this might be to do an informal assessment of whether he knows a skill, or even just ask him if he feels like he knows it, then skip right to the review section. If he shows significant weakness doing the review problems, go back and do the entire (sub)section. Otherwise, go on to the next one.

Yup, I'm with LNEsMom. Review and repeat is important for math learning.
Lisa