I've started to help my 11 year old step son with his homework and in doing so, I've noticed that his memory is very poor.

We walked through a multi-step process for adding three fractions, and after writing down the steps with examples, and slowly working through five problems using the steps, he could not tell me what the next step would be even when it was right in front of him. It was as if his memory can only contain a single step problem and cannot link together many steps in his mind.

I didn't get frustrated and tried to give him positive feedback when he would get some of the arithmetic parts of the problem right.

How do I know if this is just a motivational problem or if there is a deeper issue?