What is the biggest obstacle that Elm/Middle school english language arts teacher face in teaching immigrant/foreign student in his class?1....

Number one will end up being the biggest because it will
make growth in the areas of the other two more
difficult.

In my experience, ELL students understand you
fairly well as long as you do enough with gesturing, modelling, etc., and especially if
they are near a colleague to can explain in their native language if necessary
(frequently this isn't translation so much as helping the student to see what you are
asking in a context that is more appropriate for them, and students fluent in both
languages are AWESOME at this).

To me the two hardest
things are as follows:

1) the class being combined with
ELLs and Non ELLS, which is good for the students but makes my job more difficult when
it comes to making the class successful and effective for all students,
and

2) helping ELLs learn to write well, especially in an
academic mode.  So many little things like prepositions and word order just don't
translate and it can be exeedingly difficult to get these finer points of fluency across
to the students.  Prepositions, for example, are relatively arbitrary at times, and
require the student just memorize patterns of language.  They have so many other things
going on, memorizing "to the store, to the store, to the store" (instead of by the
store, for example) is just not at the top of their priority
list.