"Our teachers teach us."
Translation:हमारे शिक्षक हमें पढ़ाते हैं।
सिखाते is fine. I think Duolingo has a problem with टीचर. Most Indians (especially from cities) make liberal use of English words while speaking Hindi (or rather 'Hinglish') but accepting too many transliterated words would perhaps defeat the purpose of Duo.
That said, I do agree that टीचर, डॉक्टर etc should probably be accepted given that it is much more common to hear them in casual conversation than their Hindi counterparts.