查询未将结果发送到数据库，没有错误消息

Question

我正在尝试编写一些代码，这些代码从一组输入标签中获取输入，这些输入标签的生成是为了让每个学生的名字都紧挨着他们。 They look like this on the page.

点击提交（位于模式底部）后，屏幕仅显示标题，据我所知，不会修改数据库。

这是我的代码，试图获取输入数据并将其发送到数据库：

$sqlListStudents = "SELECT CONCAT(last_name,', ',first_name) AS 'StudentName',student_id FROM `students` WHERE teacher_id='" . $_SESSION['userId'] . "' ORDER BY last_name ASC;";
$resultListStudents = mysqli_query($connection, $sqlListStudents) or die("Bad Query: $sqlListStudents"); 
$doc = new DomDocument;
if (isset($_POST['submitNewAssignment'])){
    $name = $_POST['students'];
    $newAssignmentName = $_POST["newAssignmentName"];
    if(empty($newAssignmentName)){
        echo "<script>alert('New Assignment Name not set')</script>";
    } else{
        $sqlNewAssignmentName = "INSERT INTO assignments(subject_id,assignment_name,teacher_id) VALUES ('2',".$newAssignmentName.",".$_SESSION['userId'].")";
        $forCount = 0;
        mysqli_query($connection, $sqlNewAssignmentName) or die("Bad Query: $sqlNewAssignmentName");

        foreach ($name as $students) {
            $grade = $doc->getElementById("studentNum".$forCount);
            $studentList= mysqli_fetch_assoc($resultListStudents);
            $sqlSelectGradebook = "INSERT INTO grades(student_id,grade,gradebook_id) 
                            VALUES(".$students.",".$grade.",
                            (SELECT gradebook_id FROM gradebooks 
                             WHERE teacher_id=".$_SESSION['userId']." AND gradebook_title='Language Arts'))";
            mysqli_query($connection, $sqlSelectGradebook) or die("Bad Query: $sqlSelectGradebook");
            echo "for loop stuck";
        }
        echo "<script>alert('The grades were added.')</script>";
    } 
}