Lisa,
I must admit that I have tried my share of math programs with my oldest son, running through a year each of BJU, Abeka, Math-U-See, Calvert, Strayer-Upton, MCP, Teaching Textbooks (2 years of this), Math Essentials, Life of Fred, and VideoText (on our third year of this). I was always looking for the "perfect" fit for my mathy son and never finding it. I wish desperately I had used SIngapore math with him, however there were no U.S. editions at that time (and I just didn't want the headache of adding in U.S. weights/measures/money etc.)
In looking back, it would have been better if I'd just stayed the course with any of these programs. Some were stronger than others, however my constant switching eventually gave my son the feeling he wasn't good at math! It also left some pretty big holes in his math learning.
So, my first advice would be to minimize switching as much as possible!
Also, in looking back, I have since realized that I wasn't as available to my son with his math as I should have been! I have remedied this with my next kiddos, and I make sure I sit and go over the lesson and stay with them to help them as they work the problems. Math is my sit down with my kids subject now!
My own oldest son was mathy, so I just let him go on his own much of the time. Eventually, when he hit bumps in the road, I couldn't help him very easily (because I hadn't stayed with him on the math journey). It is tough to just jump into various math programs on the fly (even if I have a concentration in math in my Bachelor's that allows me to be a middle school math teacher if desired).
So, my second piece of advice is to make sure you are available during your kiddos' math sessions and that you are guiding, directing, and giving every bit of help needed to help them succeed.
The next thing I realized is that math programs regularly go back over what was taught before and teach it again, more deeply at each subsequent pass. This means that I need to know that mastering the material is not the goal at every level. In many levels, simply exposing kiddos to the concept is the goal. So, if I expect mastery of every concept, my goal differs from the math text goal. This means that I'll think they need more practice to truly master something, and the text is already moving on!
So, if I digress and add more practice, then my kiddos get frustrated and so do I when they don't master a concept. More practice then equals more frustration. If I instead realize that we were just to touch on the concept as exposure, and we're coming back to it later when the child has had a chance to grow and mature more in his/her thinking, then my math experience will be so much better! So, my third piece of advice is to make sure you do not expect mastery of every concept! This is an exhausting way to learn math.
With all of this in mind, it may be possible that you can stay the course with your current program. If, instead, you are having tears every day, even with keeping in mind all I've shared above, then it may be time for a switch. With your 9 year old, you are definitely not too late for Singapore. I would give the placement test and see where to place that child and begin there.
With your 11 year old, I would also give the placement test just to see where that child will place. This will help in determining what should happen next for that child.
Placement test:
http://www.singaporemath.com/Placement_s/12.htm
Blessings,
Carrie
This is one area I really wish that we could have used Singapore for! 