i personally think that from absolutely broad perception it utterly depends on what the teacher knows. If he only knows forms because in china people were taught only forms for a long time, only after that the "true" techniques so that they could not surpass their master, then he is not fully able to teach the "real" stuff.
However if it is a good teacher with some real life experience (not dojo-macho) he should give it the real stuff and sparring, or perhaps he was taught that from his master.
I have somewehere read that Tai Chi lost many very effective techniques because old masters dies before they could teach that to anyone (simply got killed in street fighting), but i am not saying that Tai Chi doues not know how to fight.
I have seen a woman who did it for 15 years (she was 29 i think) and if she did not lie and used Tai Chi then god have mercy with those who try to stab her...
(if my opinion is utterly wrong, dont shoot me
)