If you give old IT equipment to staff or pupils, no mater what you say or give them in writing, you and your school are liable for any problems arising from this equipment. ie electrocution, fire etc. If you sell the equipment you are responsible for the end of life and weee regulations as well as any faults. It is much safer to either sell the items to an IT trader / asset recover company or donate it to charity / waste managment group.
You also find most equipment for schools must be used till it is of no further use. If it has a value for resale then it should have a value of use for your students.