The 15-year-old was one of two students from a school, completing a placement with Alan Fleischer Builders Ltd in March 2010.
He was working on a project in West Street, Sheffield, converting an upstairs restaurant into flats and extending upwards into newly-created floors.
During the HSE prosecution, Sheffield Magistrates’ Court heard that although the school’s work placement organisation had carried out a safety assessment on the building firm, it had not taken place on the site where the incident happened.
The student was working on the third floor, which was still under construction and only accessible by ladder. As he climbed down the ladder with a bucket in his hand, he fell 2.4metres landing on the floor.
Initially he carried on working but began to feel ill and was taken home. He later went to hospital and although he suffered bruising to his left side, he was discharged.
HSE said the work placement assessment allowed students to carry out general labouring duties but they were not expected to work at height.
After the incident, students were stopped from returning to the site and all future placements to the company were suspended.
Alan Fleischer Builders Ltd, of Dinnington, was fined £1,500 with £1,320 in costs after pleading guilty to a charge of failing to ensure the safety of its employees.
HSE Inspector Medani Close said: “Young people need special consideration to protect them from risks, particularly those present when working at height, which are well-known in the industry. The employers’ risk assessment should have taken all this into account.”