Context: a teacher talking. At the same time a student not paying attention. Then the teacher asks the student what the teacher has been talking about. The student's reply:

Sorry, I was thinking (of) something else; could you repeat....

(If the student chooses not to say I missed the point)
It is OK to use THINK as a transitive verb on some occasions; but I am not sure whether the above sentence is acceptable in such a context. If the sentence sounds odd to native speakers, tell me direct.

Thank you very much.