var check_all = document.getElementsByName('student_box');

var check_flag = true;

function checkAll(_this){

    check_flag = !check_flag;

    _this.checked = check_flag;

    if(_this.checked){

        for(var i = 0;i<check_all.length;i++){

           check_all[i].checked=false;

        }

    }else{

       for(var i = 0;i<check_all.length;i++){

           check_all[i].checked=true;

        }

    } 

}

<input type="checkbox" name="student_box" id="check_all" onclick="checkAll(this)" />

<input type="checkbox" name="student_box" />