The Gemara in Eruvin 54b relates that Rav Preida would always review with one of his students 400 times and once had gone over the material 800 times until the student understood. Yeshivot have always appreciated the vital importance of chazara as a way to be koneh Torah. As the zman ended TABC talmidim were engaged in chazara for their Chumash and Gemara shiurim.