Pupils in Herefordshire and Worcestershire sat GCSE exams with some of the answers printed on the papers, it has been confirmed.
The music exam scripts were sent to a number of schools ahead of this summer's GCSE examinations, the Oxford, Cambridge and RSA Examinations (OCR) exam board said.
It is believed that pupils sat the exams before the mistake was noticed.
An OCR spokeswoman said: "OCR regrets that a printing error may have affected a small number of marks on the GCSE music question paper. We are putting procedures in place to identify the effect, if any, this had on candidates and to make allowances accordingly to ensure that no candidate is disadvantaged."
A spokesman for the Qualification and Curriculum Authority (QCA) said the examinations regulator Ofqual would now be checking with the OCR to ensure that "appropriate measures were put in place".