楼主理解有误. 句中a teacher才是表语,而good做定语修饰表语中的teacher,只是因为它被程度副词as修饰,as good才一起放在a teacher的前面.从句意上理解的话,as good a teacher as her mother意思是“和她妈妈一样好/棒的老师”.as...as中的第一个as的位置可以对比成so,即so good a teacher = such a good teacheras...as中间既可以加不定冠词和单数可数名词,当然也可以加不可数名词或名词复数,但是此时都必须还有相应的形容词修饰才行.再如：I have as many friends as you.I make as much money as you.当然,as...as中间也可以单独加形容词或副词的原级.