[Resolvido] Erro no select!

<div class="container">
<div class="span12">
    <h1><img src="images/nota.png" width="70" height="70" /> Notas</h1>
    <p>Buscar Notas de Aluno</p>
<div class="hero-unit">
    <form method="post" action="" name="lista">
    Selecione a Turma do Aluno:<br />
    <select name="turma" id="turma">
    <option value="0">Selecione a turma...</option>
    <?php
        mysql_connect('localhost','root','');
        mysql_selectdb('softacademico');
        $result = mysql_query("select * from turma");
        while($row = mysql_fetch_array($result) ){
            echo "<option value='".$row['id']."'>".utf8_encode($row['serie'])."</option>";
        }
   
    ?>
</select>
<br />
   
    Aluno:<br />
    <select name="aluno" id="aluno">
        <option value="0">Selecione a aluno...</option>
    </select><br/>
   
            <button type="submit" class="btn btn btn-primary">Buscar Notas >></button>

</form>
<?php
        $aluno_id = 0;
    if(isset($_POST['lista'])){
    $aluno_id = $_POST['aluno'];// não consigo pegar esse valor
}
   
   
if($aluno_id != 0){?>
<table class="table table-striped table-bordered">
<thead>
<tr>
    <th class="span1"><center>Aluno</center></th>
    <th class="span2"><center>Valor</center></th>
    <th class="span2"><center>Turma</center></th>
    <th class="span3"><center>Disciplina</center></th>
    <th class="span1"><center>Bimestre</center></th>
    <th class="span1"><center>Feedback</center></th>
    <th class="span1"><center>Editar</center></th>
    <th class="span1"><center>Apagar</center></th>
</tr>
</thead>
<tbody>
<?php
$lista = $daonotas->listaNotas($aluno_id);
    for($i = 0; $i < sizeof($lista); $i++){
    $nome = $daoalunos->buscaNome($lista[$i]->aluno_id);
    $turma = $daoturmas->buscaNome($lista[$i]->turma_id);
    $disciplina = $daodisciplinas->buscaNome($lista[$i]->disciplina_id);
   
?>
<tr>
<td><center><h6><?php echo $nome ?></h6></center></td>
<td><center><h6><?php echo $lista[$i]->valor ?></h6></center></td>
<td><center><h6><?php echo $turma ?></h6></center></td>
<td><center><h6><?php echo $disciplina ?></h6></center></td>
<td><center><h6><?php echo $lista[$i]->bimestre ?></h6></center></td>
<td><center><h6><?php echo $lista[$i]->feedback ?></h6></center></td>
    <td>
        <a class="btn btn-block btn-info" href="<?php echo 'editar_nota.php?id=' . $lista[$i]->id;?>">
        <i class="icon-pencil icon-white"></i>
        </a>
        </td>
        <td>
        <a class="btn btn-block btn-info" href="<?php echo 'excluir_nota.php?id=' . $lista[$i]->id;?>">
        <i class="icon-remove icon-white"></i>
        </a>
        </td>
</tr>
<?php } ?><!--fechamento do for-->

    </tbody>
</table>
<?php } else{echo "Nada Consta!";}?><!--fechamento do if-->

 

    <center><a href="cadastro_form_nota.php"><img src="images/nota2.png" width="80" height="80"/></a></center>
    <center><a href="cadastro_form_nota.php">Cadastrar Nova Nota</a></center><br/>