Always be on the look out for tears of frustration, so as to all the child some break. No one learns well enough when confused. At this point both concentration and effective learning are lost. But if you are sure that the tears are merely excuses to skip the homework, pretend to abandon him with the worksheets and let him sweat it out!
At the grassroots level, teachers in schools are given a packed curriculum for the year. Schools try to teach the students a number of procedures without delving much into its finer details. Hence, the student is left in a confounding position as to when a particular procedure must be used. The key ingredient to understanding math is constant practice and math assignment help. Unfortunately, this is not a common scenario among the popular math classes.
However, get back to your child afterward to find out how far it has gone - math can be very frustrating, especially if the child lacks a strong foundation in the topic it is working on.
We are all aware that in academics, Math is one of the toughest subjects since it involves numbers and a lot of solving. It makes you think and rationalize every detail of your solution.