Some infants spend only 12 minutes a day on maths lessons while junior schools sometimes devote as little as 16 minutes to the subject.
This revelation will reinforce the Government's conviction that many primaries need to spend more time on pupils' number skills. But the National Foundation for Educational Research team who produced the findings stressed that maths is not being neglected in most infant and junior schools.
In fact, in other cases it dominates timetables, with some headteachers questioned by the researchers claiming that their pupils were spending up to eight hours a week on maths.
Last month the Government's numeracy task force recommended that all primary children should take part in a 45-60 minutes maths lesson every day. The NFER has, however, found that, although many primaries are already achieving or exceeding that target, the time allocation can vary tremendously.
At key stage 1 (five to seven-year-olds) maths can occupy between 60 and 450 minutes per week and at key stage 2 (seven to 11) there is a similar range - 80 to 480 minutes.
Sue Harris, one of the researchers, said: "One reason for the sizeable differences may be the difficulty in quantifying the time allocated when some work is covered in mathematics lessons and some is included in cross-curricular or thematic work. A topic such as 'Ourselves', for example, can involve a lot of measuring of pupils' heights and weights and working out the difference between the heaviest and the lightest."
Nevertheless, she acknowledged that the time ranges had been wider than expected and added: "It is worrying that some schools are spending so little time on maths, but you also have to look at the number exceeding the targets. Perhaps we should celebrate that finding and the fact that the median time allocations were four hours at key stage 1 and five at key stage 2."
The survey of almost 400 schools was carried out in the autumn of 1996.
Mathematics in Primary Schools, by Sue Harris and Zenta Henkhuzens, NFER, Pounds 8. A summary is available on the Internet: http:www.nfer.ac.uk summarymaths.htm