Nancy,

Thank you for responding to my question. DS understands the commutative property for quite some time. He figured it out on his own. I have seen where parents report on the internet that their children were marked wrong for writing the equation for an array *backwards* even though the children tried to explain the commutative property to the teachers.

When I do multiplication, I actually think the PS way as in 3x7 would be 3 sets of 7 ie 7+7+7. My understanding w/ RS is that 3x7 is 3+3+3+3+3+3+3. I believe Singapore math also does the PS method. Now that I'm doing the RS method, that one makes perfect sense to me as well. Can you point me to some literature explaining that the RS way is the mathematically correct way in case DS's teacher questions it? She is very open to new ideas so I'm not worried so much about this but I thought I'd see what other afterschoolers might have done in this situation.

Sybil

Dear Sybil,

Here are a few more explanations from Dr. Cotter for you to consider as well as share with your child's teacher.

"In adding, subtracting, and dividing, we start with a number and then do something with it. For example, 7 + 5 is 7 with 5 added to it. So, multiplication should be 7 and then duplicate it. The Japanese and Montessori also do it as 7 x 5 meaning 7 five times.

There is another reason. On a coordinate system, we always go horizontal first and then vertical. So, for 7 x 5, it is across 7 and then down (or up) 5."

I hope this helps explain the RS way of "seeing" and processing math and why it makes sense to do it this way. However, as Nancy said, you might want to check what your state tests are looking for, even though in the end it's not what the test says, it's how much math our children understand, along with their ability to reason and problem solve.

Thank you for your post.

Sincerely, Rosine

Rosine,

Thank you so much for responding. I've decided to keep moving w/ RS method and deal with any problems as they come up!

Regarding Japanese method for teaching multiplication. I have Singapore Primary Math 1B. In it, , for ex: 4x3 is illustrated as 3 flowers in each of 4 pots (3+3+3+3). The RS method would be 4 taken 3 times ie 4+4+4.

Anyhow, I'm not obsessing over this lol. I just have a keen interest in teaching math!