with是介词。and是连词,连接两个对等的成分。
A student with his classmates is running now.一个小男孩和他的同学正在奔跑。这里主语是a student,而with his classmates只是介词短语,这里可以看作主语a student的定语。
A student and his classmates are running now.一个小男孩和他的同学正在奔跑。这里主语是a student and his classmates,是and连接的两个并列部分。
with连接的词做主语时谓语动词是就远原则
如
He with his classmates often plays basketball after school.
and 连接的词做主语时谓语动词用复数
如
He and his classmates often play basketball after school.