把这句翻译成英语，很简单

Suddenly, I saw our dear boss standing at the gate of the classroom!

suddenly， I found our dear boss standing at the door of class!!
如果你要表达的是“老班”的话，就把“boss”改成"guidance counselor"就行了

Suddenly,I saw our dear boss standed in front of the classroom.

Suddenly, I found our dear boss standing out side of the classroom.

All of a sudden, I saw our dear boss standing at the door of the classroom.