Este es mi view:
<?php
echo form_open('evals/proc_group');
echo form_checkbox('edu_level[]','1', in_array('1', $educational_levels)); echo form_label ('Infantes', 'infant', array ('class' => 'checkbox_label'));
echo form_checkbox('edu_level[]','2', in_array('2', $educational_levels)); echo form_label ('Maternales', 'mater', array ('class' => 'checkbox_label'));
echo form_checkbox('edu_level[]','3', in_array('3', $educational_levels)); echo form_label ('Preescolares', 'prees', array ('class' => 'checkbox_label'));
echo form_checkbox('edu_level[]','4', in_array('4', $educational_levels)); echo form_label ('Kindergarten', 'kinder', array ('class' => 'checkbox_label'));
?>
<input type="hidden" name="eval_id" value="<?php echo $evaluation->id ?>" />
<div class="clear"></div>
<?php echo form_submit('mysubmit','Guardar Grupo'); ?>
<?php echo form_close(); ?>
<div class="clear"></div>