Oh, no! I'm afraid that I'm guilty of the same behavior. Many of us tend to lose our focus when we are not interested in a subject, we are tired, we aren't learning in the right mode, or we get into the habit of losing ourselves and tuning out the world around us. So no, he may not be bored. And no, your son's loss of focus does not mean that you are a poor teacher.
You and I both know that an eight-year-old does not have all the answers. Based upon your email, your son may have developed a habit. Being focused is hard work at any age. You have various options, all of which I have tried. Here they are:
1) Try sitting beside your son if you are in the habit of sitting across from him and talking to him. Think about talking with him as you sit beside him. Talking with him means starting with a question. "What do you think we are about to learn? What do you already know about XYZ?"
2) Give him the lesson and tell him to ask for help only if he needs help. Some children prefer to puzzle out lessons on their own. That may be his learning style. Sometimes we tend to over-explain, but usually children are more receptive if they try on their own and then come to us for help. If he makes the effort to puzzle the lesson out on his own, he may make mistakes. Correct the mistakes with him. Ask him why he chose a particular answer or response. This also helps you discover how he thinks and where he tends to go astray in the learning process. This type of reflection benefits both of you.
Sometimes I use this technique with my high school students who think they would prefer to chatter instead of listening to the explanation of an assignment. When I stop explaining because they are no longer listening, they realize that they don't know what to do next. Then they ask for the explanation.
3) Explain in very short segments, as short as you can get. Then let him work up to the point where he will need another explanation. (This is not often the best option, but you can try it. It works best if your child has difficulty with multi-step situations. The difficulty lies in breaking down the explanation and determining where he should stop.)
4) Mix up explanations with self-directed work. "Do this review drill first, and then when you have completed it, I'll explain what you will do next." This sounds as if it won't work, but the child has the first accomplishment completed and is awake and alert enough to continue. The review drill gets him going, and inertia keeps him going because it will take more effort for him to shut down. He will already be in intellectual motion. In addition, psychologically, he is coming to you when he is ready for the next step, which is a different experience than you trying to get him going immediately with something that requires high concentration.
This last method works well for me in the middle school classroom. I have a review on the board for my students to begin as soon as they sit down. It's a warm-up activity to get their brains functioning and a review at the same time.Then we simply keep going as I add something similar but new.
5) If your son is not an auditory learner, he needs something to do or to look at for explanations. I cannot focus and remember auditory directions, but draw me a map, and I will sit up and pay attention and remember what I have seen. Perhaps drawing your explanations will help? Or using hand motions or written directions?
My students love to learn about poems by pantomiming the words. They learn grammar jingles by getting up and dancing to the beat. I say one line, and they repeat it with their own creative movements, and they learn those jingles quickly.
I hope this information is helpful.
God bless you. Meeting this challenge is possible for both you and your son and will likely open up new learning experiences.