EDUCATION Secretary David Blunkett this week admitted for the first time that secondary-class sizes had grown under Labour. But he said the Government had kept its pledge to reduce numbers in infant classes. Latest provisional figures from the Government showed the average size of classes in secondary schools rose from 21.7 to 21.8 between January 1998 and 1999. Statistics show that this is a continuation of a trend of a .1 per cent rise over the past 10 years. For under-16s class sizes grew from an average 23.6 to 23.7. In primary schools the average size of key stage 1 classes fell to 26.5 in January, compared with 27.1 last year. At key stage 2 the average remained about the same at 28.3.