<form action="WordPress/calculation.php">
    <input type="text" name="year">
    <select name="teacher">
        <option value='0' default>Все</option>
        <?php
            $teachers = $wpdb->get_results("SELECT * FROM wp_users;");
            foreach ($teachers as $teacher) {
                echo "<option value='".$teacher->id."'>".$teacher->last_name."</option>";
            }
        ?>
    </select>
    <submit value='Посчитать'>
</form>


calculation.php
<table>
<?php
    $year = htmlspecialchars(trim($_POST["year"]);
    $teacher = htmlspecialchars(trim($_POST["teacher"]);
    if ($teacher == "") {
        $teachers = $wpdb->get_results("SELECT * FROM wp_users;");
        foreach ($teachers as $teacher) {
            $articles = $wpdb->get_results("SELECT * FROM wp_articles_for_pps ".
                    "WHERE id_prepod='$teacher' AND year='$year';");
            $value = 0;
            foreach ($articles as $article) {
                $indicator = $wpdb->get_row("SELECT * FROM wp_indicators ".
                    "WHERE id_index='$article->id_index';");
                $value = $value + $indicator->coefficient*$article->amount;
            }
            echo "<tr>"
            echo "<td>$teacher->last_name</td>";
            echo "<td>$value</td>";
            echo "</tr>"
        }
    } else {

    }
?>
</table>