Lǎoshī yī biàn biàn de jiěshì, xuéshēng cái míngbái le.
The teacher explained it over and over until the students finally understood.
Tips
grammar
一遍遍 is formed by reduplication of the measure word 遍 (biàn, meaning 'a pass/time through something from start to finish'). It emphasizes repetition. Compare 一次次 (yīcìcì, time after time) which uses 次, a more general counter.
