Tenses/Verb Confusion

Hi,

Yes, many people I taught confused this.

While there are many possible answers to your question (depending on how well a student knows English), let me answer it in this way:

The Present Simple describes routines and permanent situations. In "The students are usually taught by Mrs Monty" the word "usually" tells us that this situation has repeated multiple times and is expected to repeat in the future - therefore it's a reoccuring (permanent) situation.

Apart from the usual use of the Present Continuous ("I'm watching TV"), we can express temporary situations - like in the example you gave - something that has just begun and is often expected to go away in the future ("More and more people are buying plasma TVs (Hell, why do I like example with TV so much...)".

And again, in the second part of your example, there is a nice tip for us ("this week"). A student must realized that this time adverbial is not "compatible" with the Present Simple because "this week" has nothing to do with "reoccurring".

"Taught" is used here because it's in the passive mood which transforms the base form of the verb into the past partiple ("Gone","taken" and so on).

If we were to cope without the present participle, we could rewrite the sentence as follows: "Mr Tanzer is teaching them this week". However it does sound a bit different.

In the end we must remember that verb tenses are mainly to convey an idea - the way he/she feels about a situation. I guess that summarizes the answer to your question.

You might want to read more in these sections:

Present Simple
Present Continuous

If any questions, don't hesitate to ask.