He was expelled from school for fiddling with the exam results.

fiddling 是动词 fiddle 的现在分词形式。fiddle 本意是"摆弄、拨弄"，引申为"篡改、伪造"，常指对文件、数据等做不正当的改动。在句中表示"篡改考试成绩"的行为。