English education at primary school level in Japan is usually very poor quality. Most primary school level teachers are not able to speak English well (or at all). The vast majority of native speakers in the classrooms are not qulaified teachers, do not have a certificate to teach at a primary school, and are therefore usually used as an assistant. The assistants role could vary greatly between schools and BOEs, but it is not uncommon for them to just entertain the kids and repeat something when the Japanese teacher tells them to.
They would need more qualified and certified English speaking Japanese teachers to improve the situation, and since primary eduaction is very broad with teachers teaching a wide range of subjects, it seems unlikely that there would be enough to go around.
Creating a uniform syllabus is a good idea, though, and would certainly help.