More than 1,200 primary school youngsters in Kirklees are being taught in overcrowded classrooms.
And over 300 in Calderdale are also in classes with more than 30 pupils.
New figures from the Department of Education show there have been some improvements in average class sizes across England, but many children are still taught in classrooms deemed “overcrowded”.
Some 8.8% of children in Kirklees are taught in classes exceeding the statutory limit of 30 pupils - while one school, in Birstall, has a class of 36.
According to the figures, 9,353 Key Stage 1 pupils - 11.8% - across West Yorkshire are taught in classes of more than 30. This is a slight improvement on 2015, but is more than twice the national average of 5.8%.
Fieldhead Primary Academy in Birstall had an average class size of 31.3 and was one of only 10 schools in the country to have a class with 36 or more pupils. The class in question had exactly 36.
Helme Church of England Voluntary Aided Junior and Infant School, near Meltham, has an average class size of 33, the largest in Kirklees, and Heptonstall Junior Infant and Nursery School has Calderdale’s highest average class size, at 31.
Although there are many schools in the area which have class sizes above the legal threshold of 30, in the majority of cases this does not make them unlawfully large, as there are a number of exemptions that can be applied where classes can still be considered lawful despite exceeding 30 pupils.
Bradford has the largest figure for West Yorkshire, with more than 19% of youngsters in classes of more than 30. Leeds is next, with 11.5%.
Across the whole of England 95,208 primary pupils are being taught in classes greater than 30, a drop of 5.5% compared to the 100,764 in 2015.
