Because of his being late for school that he was punished by

强调句? 个人认为属于强调句.
强调句 - 常用句型
1. 陈述句的强调句型
It is/ was + 被强调部分（通常是主语、宾语或状语）+ that/ who（当强调主语且主语指人）+ 其他部分.
例子 It was yesterday that he met Li Ping.
2. 一般疑问句的强调句型
同上,只是把is/ was提到it前面.
例子 Was it yesterday that he met Li Ping?
3. 特殊疑问句的强调句型
被强调部分（通常是疑问代词或疑问副词）+ is/ was + it + that/ who + 其他部分?
例子 When and where was it that you were born?
4.not … until … 句型的强调句
A. 句型为：It is/ was not until + 被强调部分 + that + 其他部分
普通句：He didn't go to bed until/ till his wife came back.
强调句：It was not until his wife came back that he went to bed.
B. 注意：
此句型只用until,不用till.但如果不是强调句型,till, until可通用；因为句型中It is/ was not ... 已经是否定句了,that后面的从句要用肯定句,切勿再用否定句了.
5.谓语动词的强调
A. It is/ was ... that ... 结构不能强调谓语,如果需要强调谓语时,用助动词do/ does或did
Do sit down. 务必请坐.
Do be careful when you cross the street. 过马路时,务必（千万）要小心啊!
B. 注意：
此种强调只用do/ does和did,没有别的形式；过去时用did,后面的谓语动词用原形.