Dropping science tests in primary schools may be behind the country's "stagnant" performance in the subject in international rankings, Ofsted has warned.
The watchdog also says it has found that some primary schools have prioritised English and maths over other subjects, and that the quality and quantity of science teaching has reduced.
In her third annual report, Ofsted chief inspector Amanda Spielman says that certain disincentives have led many primary schools to limit science teaching.
Annual report: Ofsted hits back against schools 'narrowing education'
And she also says that there have been difficulties in ensuring that teachers have sufficient scientific knowledge to teach it well.
But Ms Spielman adds that schools have enough time in the timetable for English, maths and science.
Ofsted warning over science scores
She illustrates her point using the latest findings from the Organisation for Economic Cooperation and Development's Programme for International Student Assessment (Pisa) study.
Ms Spielman says: "The latest Pisa findings show that England has made some gains in maths and reading. That’s good news. But we should not ignore stagnant outcomes in science.
"And this may come back at least in part to what happens in primary schools.
"Subject-level inspection and key stage 2 science tests were removed 15 years ago and 10 years ago, respectively.
"We know from the Department for Education’s sample test that key stage 2 science achievement has plummeted since these control levers were removed.
"And more recently, our own primary curriculum work has shown us that subjects outside the core of maths and English are often weak, and that includes science.
"Secondary schools are now having to teach most children science from a lower starting point."
In the annual report, Ms Spielman suggests that Ofsted's new curriculum-focused inspections could halt the decline of subject standards.
She says: "This erosion shows what can happen when neither inspection nor testing look below the surface at subject level, and the importance of the curriculum focus in our new framework."