As soon as they learn a new math concept, they understand it quite well. Sometimes they are ahead of teachers and parents and pick up complex math concepts on their own. On the other hand, many children must work to perfect their math facts.
Simple addition can be a struggle.
Check the homework, talk to the teacher for starters. If the child is showing signs of struggling with simple equations, even after he or she has learned adding in school, a little extra effort may be needed. A child who does not know the answer may try to slowly count on fingers, or may utter a pure guess in the hopes of being right. Or he or she may want to do something else. Reward even the small steps and stay patient.