I would disagree with Lance there. He is making the classes more interesting to them. The work he is doing is an end to that means. But having said that, I think that 'for' also sounds OK.

Hi Niwantha, Both prepositions confer different meanings. Sentence 1: This is the first time I come across this theory. It is really interesting TO me! When something is interesting to you, it stimulates your interest. Sentence 2: I strive hard to make my lessons interesting FOR my students. Here, someone is investing time and energy to cause someone else to feel interested. Both options have are very similar and some people may even use it interchangeably. However, "for" incorporates the meaning of (i) someone else who stirs an interest in you OR (ii) providing a service or supporting someone. Since John is doing something FOR his students, the preferred answer is "for". Reference: You may wish to click on this URL: http://www.macmillandictionary.com/dictionary/british/for and read #1 on the purpose of "for" (to help or benefit someone/something). Hope this helps. Cheers, Lance

I completely agree. For is the best answer because the teacher is making something interesting for the students.