He said that while primary classes had shrunk slightly there were now 71,000 more secondary pupils and 2,000 more juniors in classes of more than 30.
The minister told ITV's Dimbleby programme: 'We have reduced the proportion of large classes for the first time in 10 years. The pupil-teacher ratio has improved - only marginally, but marginally.'
He also pointed out that the improvement had come after two years of 'fairly tight' funding. Mr Blunkett said the while Labour's manifesto promised to cut class sizes for five-to-seven year olds to under 30, the party had been aware that secondary school class sizes would go up.
Theresa May, the Tory education spokeskwoman, said: 'Nursery, junior and secondary school class sizes have all gone up. It's important that large classes aren't just shunted up the school.'