$args = array();
    $args['s'] = $_REQUEST['search'];
    $args['tax_query'] = array( 'relation' => 'AND' );
    $args['meta_query'] = array(
        'relation' => 'OR',
        array(
            array(
                'key' => 'pt_assessment',
                'value' => 'rebel',
                'compare' => 'LIKE'
            ),
        ),
        array( 'relation' => 'AND' ),
    );

    // collect filter data
    // apply post types
    if ( array_key_exists( 'types', $_REQUEST ) && is_array( $_REQUEST['types'] ) && count( $_REQUEST['types'] ) > 0 ) {
        $args['post_type'] = $_REQUEST['types'];
    }

    // apply grade filter (if any)
    if ( array_key_exists('grade', $_POST) && strlen( $_POST['grade'] ) > 0 ) {
        $args['meta_query'][1][] = array(
            'key' => 'pt_grade_level',
            'value' => $_POST['grade'],
            'compare' => '=',
        );
    }

    // apply content area filter (if any)
    if ( array_key_exists('contentArea', $_POST) && strlen( $_POST['contentArea'] ) > 0 ) {
        $args['meta_query'][1][] = array(
            'key' => 'pt_content_area',
            'value' => serialize( strval( $_POST['contentArea'] ) ),
            'compare' => 'LIKE',
        );
    }

    // apply standard filter (if any)
    if ( array_key_exists('standard', $_POST) && strlen( $_POST['standard'] ) > 0 ) {
        $args['meta_query'][1][] = array(
            'key' => 'pt_standard',
            'value' => $_POST['standard'],
            'compare' => '=',
        );
    }

    // apply PD Course taxonomy filter (if any)
    if ( array_key_exists('pdCourse', $_POST) && strlen( $_POST['pdCourse'] ) > 0 ) {
        $args['tax_query'][] = array(
            'taxonomy' => 'pd_courses',
            'field' => 'id',
            'terms' => $_POST['pdCourse'],
            'operator' => 'IN',
        );
    }

    $loop = new WP_Query( $args );