Is it permissible to give private lessons to females at home in the presence of a guardian?

It is permissible to teach and to do additional work if it adheres to the strictures of Sharia, which include: the female students who are not mahrams observing hijab in front of the male teacher, lowering the gaze, adhering to Islamic manners, not speaking in a soft or alluring tone, limiting conversation to what is necessary, and being wary of khalwa (private seclusion) with a non-mahram woman. If everyone adheres to these strictures and there is no fear of fitna (temptation or discord), then there is no objection to it.