Well yes. Sometimes a much higher ranking student will work with a much lower ranking student. In a case like that the higher ranking student tones it down to match the level of the lower ranking student and the idea is for the higher ranking student to help out the lower ranking student. But, most of the time you will be training with somebody at or around your same rank. That way you don't have to tone it down.
Not in either of my arts. When we train Aikido, there may be everything from a 5th or 6th kyu on the mat to a nidan. They are all expected to train together and do the same techniques....Same with MSR. Sensei will demonstrate the technique...he will turn, look at everyone and motion to practice. You then take turns being uke or nage and do 2 techniques on each side, alternating every fourth between uke and nage roles, until Sensei claps. You will practice 2 separate techniques with each partner, and then it is expected that you change partners. YMMV.