Maybe reminding him of his father's failure can make him really angry and fight not to be as he..but it would also increase the child's hatred for his husband and it's nor good for the health of the child, moreover the child would never learn to forgive..i think she should think of other ways to motivate him like praising him or giving him special treats for his good work!!

Children should be given good example and keep away from bad ones, by comparing him to his dad, he would obviously turn out to be like him, she should not talk about things which her son dislike! I wonder how can she do such mistake, she is rather demotivating her son!

I think that it is not good to compare him with his dad as people has the tendency to focus on the negative sides of others.They will always find the glass half empty instead of half fill.
I think that she should find another role model for the son.

I agree with youyou that she may have to find another role model for the children.If she continues like this the child may turn out to become like his dad.She could try to use other ways to motivate the child such as using the example of a friend or a relative who has succeeded in life because of hard work and perseverance.