Clothes and shoes for young children are already exempt but a 20 percent tax is slapped on items for older children.
The tax hits clothes and footwear with maximum sizes bigger than an average 13 year old.
Critics say this penalises larger than average children and forces families to spend millions of pounds more on uniforms.
When the Brexit transition phase ends at the close of the year the UK is expected to have new freedoms to cut VAT rates without the consent of the remaining member states.
The report from the Schoolwear Association states: “School uniforms are essential items of clothing for millions of children across the country. Government should use the next Finance Bill to exempt school uniform from VAT and help keep unnecessary costs down for families.”