Odd coincidences

I taught two courses this semester with 24 and 30 students enrolled. In each course the last student listed alphabetically had a last name beginning with T. In each course the two students listed alphabetically just above the last student withdrew from the course; each of these students had a name beginning with S. In each course the student at the 25th percentile (arranged alphabetically) withdrew from the course. In each course students arranged close to each other on the alphabetical list were more likely to work together on assignments than students far away from each other on the alphabetical list.