Translation:In the opinion of the students, it is the most interesting lesson of the week.
Present tense can be used if the lessons still take place regularly. For example, if I'm halfway through the school term, I might say, "The mathematics class is the most interesting class of the week". It's a similar thing here.
If I use the present tense, I would be referring to the mathematics classes in a more general sense. Maybe the mathematics teacher is better than the other teachers, but each week the mathematics class is usually more interesting than the other classes.
If I use the past tense, I would be talking about a single class. For example the mathematics class on the 20th of January was more interesting than the rest of the classes in the week from the 17th to the 21st of January, but maybe next week it will be the history class that is the most interesting