Help appreciated.

I'm grading a 17-year-old student's hypothetical essay, and I'm puzzled about the following sentences:
"If my son were caught shoplifing, I would be very angry. After all he WAS my son; I would hate to see him go astray."
My question is: Is it acceptable to use "he IS my son?"

And how about this sentence in the same article:
"What is more important is that he knows he has done something wrong."
Should it be changed into:
"What was more important was that he knew he had done something wrong."
Hello Glee, welcome to EF.

Either the present or the past may be appropriate in these sentences. There is no way to judge without reading the context. Generally, whichever tense the narration is cast in, it should be consistent.

Here, is seems that the narrator is speaking in his/her present time (the time of writing)-- in which case they should be in present tense ('after all he is my son', if the son is still alive and not disinherited at the time of writing; 'what is more important is that he knows he has done', if the knowing is now and the bad deed is in the recent past from the narrator's standpoint).

However, I have no way of knowing if the whole story is cast in the past tense, as if the narrator were remembering, for instance. In that case, past tense may be more appropriate.

These concerns have nothing to do with the subjunctive. The subjunctive in the 'if' clause of your first sentence is non-past; it is, as you say, hypothetical.
The narrator is only 17 years old - I would think that having a son caught shoplifting would be in his hypothetical future, not present or past.
Teachers: We supply a list of EFL job vacancies
The writer is a 17-year-old, but we don't-- or at least I don't -- know the persona of the narrator.
Students: We have free audio pronunciation exercises.
Thanks a lot for your replies.

The essay topic is "What would you do if your child were caught shoplifting?" It asks a class of 17-year-old students to pretend that they are parents now. So I thought every move the 17-year-old hypothetical parent makes in his essay should be written in subjunctive mood. Doesn't that mean past tense will be more grammatical?

In the following passage, is it OK to use present tense as long as I stick to the rule of consistencey?

"If my child were caught shoplifting, I would be very sad. After all, his unlawful behavior INDICATES that I HAVE not taught him well. I would not scold him too harshly. Since I AM his father, I CONSIDER myself partly responsible for his mistake. Therefore, I would first try to understand the reason why he did this and then work out a solution to help him solve his problem. The most important thing IS that he KNOWS he HAS done something wrong and never MAKES the same mistake again."

Thanks again for your time.