Question: Is there any difference between considered to be and considered as?

For example:

* Adam is considered as a good teacher.
* Adam is considered to be a good teacher.

Answer: 
"is considered to be" is [significantly more common](https://books.google.com/ngrams/graph?content=is+considered+as%2Cis+considered+to+be&case_insensitive=on&year_start=1800&year_end=2000&corpus=15&smoothing=3&share=&direct_url=t1%3B%2Cis%20considered%20as%3B%2Cc0%3B.t1%3B%2Cis%20considered%20to%20be%3B%2Cc0) and if you look at other uses of "is considered as" you notice a key difference between the two sentences:

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> ... who **is considered as** a debtor...
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> ... the thing whose representation **is considered as** a part of the sphere...
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These uses are either telling the reader that you should (a) consider two things as equals or (b) use a particular context in order to consider something.

"is considered to be" is telling the reader how *others* consider a thing. In your example, this is much more likely to be the correct choice.

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> Adam is considered to be a good teacher. — Adam is thought to be a good teacher.
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> Adam is considered as a good teacher. — We have treated Adam as if he is a good teacher.
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The difference is subtle and not easy to explain.
There is no such thing as "considered as" 

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> Adam is considered a good teacher. 
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<http://www.thefreedictionary.com/as>

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> As is sometimes used superfluously to introduce the complements of verbs like consider, deem, and account, as in They considered it as one of the landmark decisions of the civil rights movement. The measure was deemed as unnecessary. This usage may have arisen by analogy to regard and esteem, with which as is standardly used in this way: We regarded her as the best writer among us. But the use of as with verbs like consider is not sufficiently well established to be acceptable in writing.
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