All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah and that Muhammad is His slave and Messenger.
It seems that your concern is that teaching is not your specialty and that you are wondering whether it is permissible to work in other than your (academic) area of expertise. You should know that the criterion in this regard is your ability to efficiently carry out this job. If you believe that you are able to do this job efficiently, then there is no harm in accepting it. Allaah, The Exalted, says (what means): {...And do good; indeed, Allaah loves the doers of good.} [Quran 2:195] 'Aa’ishah narrated that the Prophet said, "Verily, Allaah loves that when anyone of you does a job, he should perfect it." [Al-Bayhaqi]
However, if you fear that you may not be able to carry out this job as required, then it is impermissible for you to accept it unless the school or any other entity offers you training in order to learn how to perform the job as due.
Allaah knows best.