We could write sentences if he is no longer teaching.
"John has come to town and is teaching our students."
The Present Perfect brings the situation of 'being in town' up to NOW, the moment of speaking these words. Without a further clause or sentence, we can only guess whether he is about to leave. Hence, using the Present Progressive, which extends beyond NOW indicates he is still in town.
"John came to town and has been teaching our students."
Here, again, the Present Perfect Progressive brings us only up to NOW. So:
"John came to town and has been teaching our students. We are all sorry this is his last day with us."
"John came to town and has been teaching our students. We are all very happy he has decided to continue with us."
...as two examples.
No native speaker of English says infelicitous stuff like that.
It is ambiguous and poorly constructed, so analysing it is pretty pointless really since one would just go round in circles searching for the intended meaning through a process of disambiguation.
Thanks Paul! That's what I thought (my gut instinct), but wanted to get confirmation. I've been speaking Polish for so long I forget my English grammar!
Thanks Gervais! I get taken aback sometimes and lose my confidence when encountering surprise sentences like this. You and Paul both gave what my gut was telling me, but I wanted to make sure! Thanks to both of you once again.
Glad to help. For my part, your question was not about how 'natural' the language of the sentence is. I wanted to address your query:
"The original question came up after various simple past and present tense statements were presented and then the question, Where is John? "
...and what information about this could be derived from the tense of the verb forms.
Mr.Matthews and I have different approaches when it comes to tutoring in English.
What qualifications do you have that justify your using the term 'tutoring' to describe the approach that you take on this website?