Ошибка в строке
$query = "INSERT INTO `student`(`student_id`, `student_login`, `student_password`, `student_first_name`, `student_last_name`, `student_phone_number`, `student_gender`, `original_back_school`, `original_end_time`, `original_class`, `class_Halom`, `parent_id`, `teacher_id`) VALUES ($student_id, '$student_login','$student_password','$student_first_name','$student_last_name', '$student_phone_number','$student_gender','$original_back_school',' $original_end_time','$original_class','$class_Halom','$parent_id','$teacher_id') ";
$student_id
не написано в ' '
Это должно быть похоже на '$student_id'
Фактический код будет
$query = "INSERT INTO `student`(`student_id`, `student_login`, `student_password`, `student_first_name`, `student_last_name`, `student_phone_number`, `student_gender`, `original_back_school`, `original_end_time`, `original_class`, `class_Halom`, `parent_id`, `teacher_id`) VALUES ('$student_id', '$student_login','$student_password','$student_first_name','$student_last_name', '$student_phone_number','$student_gender','$original_back_school',' $original_end_time','$original_class','$class_Halom','$parent_id','$teacher_id') ";
Это решит вашу проблему.