of course you knew you would get this answer - it depends on what the student has. if the student has:

no equipment - clearly i provide everything

radio with no buddy box compatibility - i replace the rx or xtal with my own and fly with my own tx and buddy box

radio with buddy box and xtal compatibility - i fly my tx as the master and use his/hers as the buddy box

radio with buddy box but no xtal compatibility - i fly with his/her tx as the master and use mine as the buddy box

naturally the best for me is to be able to use thier planes and my tx as the master and his as the buddy box. i fly a Hitec Eclipse 7 and since I have the spectra module, I can fly all 72 mhz channels W/O changing xtals and buddy box all futaba radios. this I think is the best set up. having them flying their own planes is the best because you can first check out the plane and trim it instead of having him/her do it. then when he/she is ready for his solo, he/she does not feel so much pressure when flying his/her own plane. using his/her tx is also very important because it is good to get to know where all your functions are. if you are running a computer radio buddy boxed all the dual rates, electronic trims still work. it's good for the student to know where things are and be familiar with his/her own radio.