The teacher and the student would both need the chat app. Either could enter questions/answers while the other is offline but the message will still be there when the other person activates his/her copy of the app.
Here are two ideas. Neither is exactly what you want to do.
You could adapt either of these to your purposes. Experiment.
There isn't any Como saber as respostas da caixa de texto, the teacher asks questions and the student responds to the question as typed by the teacher perhaps.
