meaning of "然後三個三個分成小組"
X 个 X 个分成小组 means to divide something into groups of X. So 三个三个分成小组 means to divide these students into groups of 3. But the number of groups is not necessarily 3.
The expression &quot;X 个 X 个&quot; is something like giving an example of arrangement, or the manner to process a bunch of things, such as:

把这些苹果两个两个放在一起。    # two apples together
把这些苹果一个一个洗干净。    # wash the apples one by one