I "homeschool" my four-year-old son in addition to sending him to a half-day, K-5 preschool. How should I deal with him -- and my own frustration -- when he suddenly "forgets" how to accomplish a task? His preschool teacher has also remarked on this tendency but has no advice. My son is approximately two years ahead of his age intellectually.
When you say you "homeschool" your four-year-old son, I assume you mean you teach him school-type subjects at home. A four-year-old boy who is in preschool and receives additional schooling when he comes home appears to be getting too much of a good thing. He may have the intellectual capacity of a six-year-old, but the reality is, he is only four years old and needs to do the things kids his age do -- play, explore, and have fun. While it may be gratifying as a parent to have a boy who is able to do more than his peers, there is little evidence that it is desirable or even helpful to stress early academic work with young children. Some educators even believe it may be harmful, resulting in early burnout and lack of academic success in later years.
Not knowing your child, I also do not have an answer. My first guess, however, is that this boy is simply on "overload." His young mind may be having a difficult time processing all the information being presented to him. One child may resist by having a tantrum, another may become whiny, and your son simply "forgets." How to deal with him? Relax, give him some space, put away the pencils and paperwork, go to the park, and encourage him to spend large blocks of time each day involved in creative play. Good luck!