In general, the school provides learning material for students for a certain period of time. Sometimes, the learning material can be used continually. The NRW School Act specifies the conditions in § 96. There is a certain amount the parents have to pay for additional learning material, according to NRW School Act § 96 paragraph 5. The average amount for parents of 12 to 16 year old pupils is 78,00 € per school year.
In addition, the parents have to provide the consumption and practise material.
For further information see: https://www.schulministerium.nrw.de/docs/Recht/Schulrecht/Verordnungen/VO_96_5.pdf