They said they chose our school because we are one of the best secondary schools in Mexico City.

secondary 由前缀 second-（第二）和后缀 -ary（与...相关的）组成，原意是"第二位的"，在教育系统中特指"中等教育的"。 schools 是 school 的复数形式，school 指"学校"。 secondary schools 指中等教育阶段的学校，即"中学"，介于小学和高等教育之间的教育机构。