"randomization" is not the important part here. "evenly distributing" is. It is absolutely possible to reorder the sequence fairly such that your scenario doesn

"randomization" is not the important part here. "evenly distributing" is. It is absolutely possible to reorder the sequence fairly such that your scenario doesn't occur. It could even to a human observer look randomized if you want. In a trivial example case where the effect were linear you could just switch the order back and forth, and on average every student would receive the same middle-of-group impact.