Is it permissible to buy and present what is known as "Coptic art" which bears images of the cross and Copts, knowing that the school is mixed and the student of the subject may be Christian or Muslim, and that this work may or may not be part of the curriculum?

It is not permissible to buy anything that contains the image of a cross or the worship of anyone other than Allah the Almighty. The Permanent Committee for Issuing Fatwas has ruled that it is not permissible to manufacture ornaments bearing symbols of disbelief and its emblems, such as the cross and the Star of David. Nor is it permissible to sell or buy them. What the questioner mentioned is not considered among the necessities that permit prohibited things.