Pupils are leaving primary school unprepared for the rigours of science and foreign languages at secondary level, Ofsted's chief inspector says.
Sir Michael Wilshaw said the focus on the "three Rs" had pushed other compulsory subjects "to the margins of the curriculum" in primary schools.
Science and languages had become the "poor relations" of the primary curriculum as a result, he said.
The government said more pupils were taking science and languages at GCSE.
Sir Michael said, in his monthly commentary, that the government wanted most pupils who started secondary school last September to take the full suite of English Baccalaureate (EBacc) subjects, including science and a foreign language, when they sat their GCSEs, in 2020.
The EBacc is a wrap-around qualification that requires candidates to obtain GCSEs in English, maths, history or geography, a foreign language and two sciences.
Sir Michael said: "This drive to raise the academic achievement of our young people is a laudable ambition but undoubtedly a very challenging one.
"In 2015, less than half of all pupils studied a foreign language at GCSE and, although science is a core subject that should be studied by all pupils to age 16, only 74% of pupils took it to GCSE level to qualify for the EBacc.
"It seems clear that if the government's ambition is to be met, primary schools will need to lay the foundations in these subjects before their pupils move on to study them at secondary school."
