Trying to align checkboxes as buttons in Bootstrap is proving to be a challenge. The usual methods like "text-center" and "center-block" have been attempted within the surrounding divs and inputs but without success. (The unsuccessful attempts can be observed in the provided example where "text-center" and "center-block" are used frequently.)
HTML:
<div class="row grade-selection">
<div class="col-xs-1"></div>
<div class="col-xs-2 btn-group text-center" data-toggle="buttons">
<label class="btn btn-primary">
<input type="checkbox" autocomplete="off">K</label>
</div>
<div class="col-xs-2 btn-group" data-toggle="buttons">
<label class="btn btn-primary text-center">
<input type="checkbox" autocomplete="off">1</label>
</div>
<div class="col-xs-2 btn-group" data-toggle="buttons">
<label class="btn btn-primary">
<input class="text-center" type="checkbox" autocomplete="off">2</label>
</div>
<div class="col-xs-2 btn-group center-block" data-toggle="buttons">
<label class="btn btn-primary">
<input type="checkbox" autocomplete="off">3</label>
</div>
<div class="col-xs-2 btn-group" data-toggle="buttons">
<label class="btn btn-primary center-block">
<input type="checkbox" autocomplete="off">4</label>
</div>
<div class="col-xs-1"></div>
</div>
<div class="row grade-selection">
<div class="col-xs-1"></div>
<div class="col-xs-2 btn-group" data-toggle="buttons">
<label class="btn btn-primary">
<input class="center-block" type="checkbox" autocomplete="off">5</label>
</div>
<div class="col-xs-2 btn-group" data-toggle="buttons">
<label class="btn btn-primary active">
<input type="checkbox" checked autocomplete="off">6</label>
</div>
<div class="col-xs-2 btn-group" data-toggle="buttons">
<label class="btn btn-primary active">
<input type="checkbox" checked autocomplete="off">7</label>
</div>
<div class="col-xs-2 btn-group" data-toggle="buttons">
<label class="btn btn-primary">
<input type="checkbox" autocomplete="off">8</label>
</div>
<div class="col-xs-2 btn-group" data-toggle="buttons">
<label class="btn btn-primary">
<input type="checkbox" autocomplete="off">9</label>
</div>
<div class="col-xs-1"></div>
</div>
<div class="row grade-selection">
<div class="col-xs-3"></div>
<div class="col-xs-2 btn-group" data-toggle="buttons">
<label class="btn btn-primary">
<input type="checkbox" autocomplete="off">10</label>
</div>
<div class="col-xs-2 btn-group" data-toggle="buttons">
<label class="btn btn-primary">
<input type="checkbox" autocomplete="off">11</label>
</div>
<div class="col-xs-2 btn-group" data-toggle="buttons">
<label class="btn btn-primary">
<input type="checkbox" autocomplete="off">12</label>
</div>
<div class="col-xs-3"></div>
</div>
</div>
</div>
To demonstrate the issue, I have created a Fiddle with one of the divs highlighted in a different color for clarity on the lack of alignment: https://jsfiddle.net/rovh1fcw/3/
Your assistance in resolving this matter is greatly appreciated! It seems to be a simple oversight on my part.