What is ... (a noun) am/is/are/was/were to...(a verb)

be + to-infintive是一種特別的用法，有幾種意思：
１）是表示責任或必要，如：
I am to inform you that...... (i.e. I have been told to inform you)我受託通知你．．．（所以有責任）
２）表示意願；打算，如：
They are to be married in May．他們打算於五月裏結婚
３）表示可能性：
The book was not to be found.(i.e. could not be found)那書根本找不到了
４）假設
If I were to tell you假設我告訴了你（但這假設用法一定要用were）
５）（主要用過去式）表示(命運)
He was never to see his wife and family again(i.e. Although he did not know this time, he did not see them again)他從那時起就再也見不到他的妻子兒女了(雖然他當時並不知道，但是他以後沒有再看見他們)
６）表示互相的約定：
We are to be married in May.我們定於五月裏結婚
Every member of the party was to pay his own expenses.參加餐會者各人須自付餐費
７）他人所表示的意願
At what time am I to be there?我應於何時到達那兒？
８）目的
The telegram was to say that she had been delayed.電報上要說的是她已因故延遲。

這都是be + (to-infinitive)的用法，而你的例句是屬於有（１），每位學生都需要努力（責任）；希望你明白，其實你可以查一些大字典，看be的用法，也有介紹。古德明先生在征服英語，也有談論過，但因現在我手頭上沒有資料，待遲些才補上他的講論。