Students are all put in different groups according to their ability.

according 是动词 accord 的现在分词形式，accord 的意思是"一致、符合"。 to 是介词，表示方向或关系。 according to 是一个固定搭配的介词短语，意思是"根据、按照"，用于引出依据的来源或标准。