"零散地落在后头" can be translated into English as "falling behind in a scattered manner" or more naturally as "lagging behind in a disjointed/scattered fashion".
Here are two example sentences for context:
1、 Some of the students are falling behind in a scattered manner due to lack of proper guidance.
（由于缺乏适当的指导，一些学生零散地落在后头。）
2、 The team members were lagging behind in a disjointed fashion, unable to keep up with the pace set by the leaders.
（队员们零散地落在后头，无法跟上领队设定的步伐。）