.to gauge the effect that this had on a range of issues relating to education
这里that和后面的句子是修饰谁的?effect吗?on是什么作用呢?是had \on a range还是had on \a range
原句是It compared children born in September – at the start of the academic year – to those with birthdays in August to gauge the effect that this had on a range of issues relating to education .