You should all know this is inline scripting and is not a good practice at all...with that said you should definitively use javascript or jQuery for this type of thing:
HTML
Online Student PortalJQuery
var button_my_button = "#myButton";
$(button_my_button).click(function(){
window.location.href='Students.html';
});
Javascript
//get a reference to the element
var myBtn = document.getElementById('myButton');
//add event listener
myBtn.addEventListener('click', function(event) {
window.location.href='Students.html';
});