He says the reasons for differences between high schools is something that teachers are best positioned to explain.

【翻译】他说，高中学校之间的差异，教师最有资格解释其原因。

【分析】此句，the reasons is，显然不合乎语法。改正的办法，要么the reasons are，要么the reason is。

be best positioned to do sth. ：最有条件/资格/能力/可能做某事。