The 15-year-old girl, who cannot be identified, was arrested and bailed on suspicion of inciting racial hatred in a school incident two weeks ago.
A 14-year-old boy was then arrested on Tuesday on suspicion of making threats. He was also released on police bail.
The teacher said pupils at the Sandwell school were shocked by the incident.
He said he had spoken to the rest of the school on Thursday about the developments.
"I wanted them to be aware and have an accurate interpretation of the events of the past week," he said.
"I was pleased the majority of them were shocked and appeared not to be aware of what had happened and not to have been involved in it.
"I am personally very disappointed that this should have happened in our school."
Hafiz Ghulam Rasool, who is a member of Sandwell's Imams council, said the burning of any sacred book was an "abominable act".
The book involved was an English language version of the Koran, the school said.
Mr Rasool added that it was even more worrying that it might have happened on school premises.