穿着校服参加老师的葬礼
[chuān zhe xiào fú cān jiā lăo shī de zàng lĭ]
Which means attend a teacher's funeral in school uniform. This reflects the respect paid to teachers (it might indicate reverence by dressing appropriately, even formally) from the depths of students' hearts at sad times or events like funerals while recalling campus memories/stories during school days. But in different cultural contexts or personal experiences, such settings might evoke various emotions, not necessarily restricted only to solemn/sadness.