Decomposing numbers into pairs, Duplo activity

This week, we're working on decomposing numbers into their pairs.  For example, three and seven make ten. 

Our materials are pretty simple.  We are using the same box of magnetic numbers that I showed you in my post, Addition at the Fridge, a metal board that allowed us to have our lesson on the front porch rather than in the kitchen, and several Duplos.

The first time I presented this lesson, I showed him how to do the exercise using the number five, then coached him through breaking down the number eight.  Yesterday, when I shot these pictures, I simply gave him stack of four blocks and told him to break it down "like we did before."

He broke down the blocks and built them in the way that you see, before setting up the equation.

When he was finished, I told him to keep the equation and find another one, which he did, three more times.  Once he had finished all the possible equations, I told him to check his work by counting from zero through the number he was working on (four).

This lesson addresses Common Core objective K.OA.3.   Decompose numbers less than or equal to 10 into pairs in more than one way, by using objects or drawings, and record each decomposition by a drawing or equation.

 I am wondering if I should have presented this concept before addition and subtraction.  It seems like mastering this first, would make addition and subtraction very obvious.  On the other hand, confidence working with equations was a nice bonus to doing this lesson second.  What do you think?