"The implementation of mandatory English in the 5th and 6th grades of elementary schools in Japan is just one part of the revision of the Course of Studies (Gakushu Shidou Youryou), which normally takes place once in ten years in Japan. The revised Course of Studies has been officially released on March 28th and it has been announced that this new Course of Studies (for elementary school) will be implemented in April, Heisei 23 (2011) . The Ministry of Education normally sets a two year transition period for schools to prepare for the changes, which has also been announced for the upcoming revision. As a result, schools can start making changes (e.g. starting English in the 5th and 6th grades) from April 2009. This may be why you are hearing different dates from different sources. Another possibility is that different local BOEs making decisions for increasing the number of hours of English in their areas in order to start the preparations early. This is also possible because English Activities is already part of Sogotekina Gakushu no Jikan and schools are left to decide the number of hours they plan to provide each year.
For a source of the official announcement, you can read the Education Minister's official statement concerning the implementation of the revised Course of Studies" (only provided in Japanese). [Brett: yes, the last course of study wasn't officially translated until a good year or so after it came into effect. At the time, my translation was the only one available to most English teachers.]
Now it seems that the government's attempts to do this on the cheap are not getting much buy-in from the public. The Daily Yomiuri notes that a survey had "70 percent of the respondents saying professional English teachers are needed to ensure the language is taught effectively.... and and 58 percent said they wanted native English speakers to teach at primary schools. On the other hand, less than 20 percent of respondents supported measures the Education, Science and Technology Ministry is considering introducing, such as educational CDs and DVDs and English-speaking volunteers who would act in a supporting role."
In a wealthy country like Japan, I agree with the parents, but in poorer countries, I think a good deal could be achieved with graded readers, CDs, and a little training for the teachers.