echo "<hr>
<form method='post'>
Отметьте пришедших учеников:<br>
<table align=center>";
print_r($GLOBALS);

$sqlu = "SELECT 
s.id, 
s.name AS `student_name` ,s.released,
(SELECT date_duty FROM student_duty WHERE student_id = s.id ORDER BY date_duty DESC LIMIT 1) AS date_duty,
(SELECT student_id FROM student_duty WHERE student_id = s.id ORDER BY date_duty DESC LIMIT 1) AS student_id,
(SELECT class_id FROM student_duty WHERE student_id = s.id ORDER BY date_duty DESC LIMIT 1) AS class_id,
(SELECT id FROM student_duty WHERE student_id = s.id  ORDER BY date_duty DESC LIMIT 1) AS id

FROM `students`  AS s  where released = 'no'   ORDER BY date_duty asc,name asc
";
$resultDutygu = mysql_query($sqlu);


while ($rowgu = mysql_fetch_assoc($resultStudents2)) { 

echo "<tr><td><input type='checkbox' name='student_id[]' value='".$rowgu['id']."'>".$rowgu['name']."</br></td></tr>";


};
echo "

</table>
<input type='submit' name='sido' value='Забить'>
</form>";

if (empty($_POST['student_id']))
{}
else
{

while ($rowgu = mysql_fetch_assoc($resultStudents2)) { 

$sqlInsertu = "INSERT INTO `student_duty` VALUES(null, '$_POST['student_id']', '+', '')";
mysql_query($sqlInsertu); 
echo $_POST['student_id']; //тест

};

};