Children swapped their pencils for construction tools when they were given an insight into civil engineering.
Pupils from Pope Paul Catholic School, in Baker Street, Potters Bar, were given an all-day civil engineering exercise by Skanska Balfour Beatty.
The company are currently upgrading the M25 in Hertfordshire and Essex between junctions 23 (South Mimms) and 27 (M11) on behalf of the Highways Agency.
Year 4 pupils were divided into groups and had to build a free-standing arch out of paper and adhesive tape which they could crawl under to give them an insight into construction.
Employees Hari Dohesvaran, Andy Graham and Ami Martin were on hand to explain the upgrade and to judge the entries.
The winning children received WH Smith vouchers and every child received a Skanska Balfour Beatty tote bag.
Their teacher, Margaret Joyce, said: "The school really appreciated the day’s exercise as it helped the children with maths, arithmetic, teamwork and time management. It was also great fun."