The Ministry of Education has announced findings that 28,511 foreign children currently in state schools have insufficient Japanese ability for daily conversation. That's 38.4% of the 74,214 foreign pupils registered as of May 2011. It represents a small drop of 64 pupils compared with a similar investigation results revealed in 2008. The survey was actually conducted in September 2010 so it is possible that the numbers might now be lower following the triple disasters in March. According to the findings, pupils are attending 3,831 elementary schools, 2,157 high schools, 367 senior high schools and some specially-funded institutions across the country. The Ministry also classified the children by mother tongue, the major languages being: 9,477 Portuguese; 6,154 Chinese; 4,350 Tagalog; 3,547 Spanish; 1,151 Vietnamese; 751 Korean; and 717 English. Aichi has by far the largest population of such students: the prefecture's 5,623 is approaching twice the number of second-placed Kanagawa's 2,990 pupils. Tokyo and Shizuoka occupy the next two spots with 2,705 and 2,485 respectively.
Even before the disaster, Japan's foreign population recorded two years of decline so it perhaps wasn't unexpected that the numbers recorded in this survey did not actually rise. However, the Ministry noted that the numbers were spread across a greater number of schools, including those with little ability to handle these students. Consequently, they continue to look at ways to support schools in helping pupils to handle the curriculum.
Source (Japanese)