SO - 28942561

by Arun P Johny

HTML

<script src="//code.jquery.com/jquery-1.11.2.min.js"></script>
<label>
    <input type="checkbox" name="agreement">I read all the information in the red box above and followed the instructions!</label>
<br/>
<input disabled="disabled" type="submit" name="submit">

JavaScript

$(document).ready(function () {
    $("input[name=agreement]").change(function () {
        $("input[name=submit]").prop('disabled', !this.checked);
    })
})