Accessible Checkboxes Using Drupal's Form API
Try changing your code to the following, no need for the call to form_process_checkboxes.  

function my_module_block_view($delta='') {
  $block = array();
  switch ($delta) {
    case 'myform':
    $block['content'] = drupal_get_form('mymodule_form');
    break;
  }
  return $block;
}

function mymodule_form() {

  $form = array();
  $form['tests_taken'] = array(
    '#type' =&gt; 'checkboxes',
    '#options' =&gt; drupal_map_assoc(array(t('SAT'), t('ACT'))),
    '#title' =&gt; t('What standardized tests did you take?'),
    '#attributes' =&gt; array(
      'name' =&gt; 'example-checkboxes[]'
    )
  );

  dsm($form);

  return $form;


}