With just weeks to go before English becomes a compulsory subject at Japan's primary schools, doubts surround the boldest attempt in decades to improve the country's language skills, and its ability to compete overseas with rival Asian economies.

The new curriculum is to be introduced after intense lobbying from the business community, amid fears that Japan's competitive edge could be blunted unless it takes English communication as seriously as China and South Korea.

The new classes, which start in April, will be aimed at fifth- and sixth-grade pupils, aged 10-12, at all of Japan's public primary schools. The lessons will be held only once a week – or 35 times a year – with each lasting 45 minutes.

By the time they leave primary school, children should know 285 English words and 50 expressions, although the education ministry is reluctant to talk of targets.

Hiroshi Noguchi, of the ministry's international education section, said the main purpose was to ease the transition from primary to junior high school, where English has long been compulsory, and to expose young children to other cultures.

"We don't have any specific targets," he said. "The schools have been given the choice of how to structure their lessons and set their own targets. We believe children will leave knowing the basic expressions that will help them on their way with English learning."