The teacher commended the student's efforts in the project. In this sentence, what is the antonym of 'commended'?

The correct answer is criticized.

To commend someone means to praise them formally or express approval of their work. Therefore, the antonym (opposite) is to criticize, which means to indicate the faults of someone or something in a disapproving way.

While "despised" means to feel deep hatred and "applauded" is actually a synonym for commend, "criticized" is the most direct linguistic opposite in the context of evaluating someone's performance or efforts.