请分析一下这句话的语法结构What my education failed to do was to teach me

主语 what my education failed to do；谓语 was；表语 to teach me that the principal significance of such differences was that they were largely without significance
但是表语中还含有表语从句：that they were largely without significance
that the principal significance of such differences was that they were largely without significance做teach的直接宾语（宾语从句）,这个宾语从句中：the principal significance 是主语,was是系动词（谓语）,that they were largely without significance是表语从句.

What my education failed to do 是主语， was 谓语动词，后面全是表语。 表语中第一个that 引导的是宾语从句 第二个that 引导的是第一个that引导的宾语从句当中的表语从句。

主语 what my education failed to do
谓语 was
表语 to teach me that the principal significance of such differences was that they were largely without significance.

What my education failed to do （主语）was （系动词）《to teach me （that 宾语从句the principal significance of such differences(主语） was（系动词) that （表语从句）they were largely without significance）.》（to do 做表语）

赞同楼上

What my education failed to do主语从句，was to teach me that the principal significance of such differences was that they were largely without significance.两个 表语从句。表语从句里又包含了宾语从句that the principal significance of such differences