When children always have excuses for not doing well, the excuses are usually exactly what are causing the problem. They are usually right. They say they did not know what to do or did not understand. They say they forgot to do their work or say they thought they had done it right. They say they did not hear, and on and on. After a while, their excuses wear thin. It is easy for adults to get frustrated and just react. A better reaction is to take your youngster at his word. It is probably the truth.
Listen to your child's excuse. Say, "I believe you. What you told me is exactly what happened. I also want you to learn the difference between an excuse and a reason. A reason is an explanation. An excuse makes it sound like it was okay. Your not doing well is not okay. Now that you understand the reason, we are going to figure out a way to keep it from happening. You say you did not do well because you did not hear the assignment. Let's talk about how to be sure you hear and understand assignments."
Just be sure you stay calm and focused on the reason. It is a problem to solve and not an excuse for you to blame your child.