Data not inserted in sqlite

I'm starting now on Android, I went to do a test of insertion of data in the bank, but the data is not inserted, I may be mistaken at some point, follow below the code:

   protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_lista_alunos);

Class responsible for introducing students to the list:

    AlunoDAO dao = new AlunoDAO(this);
    List<Aluno> alunos =  dao.buscaAlunos();
    dao.close();

    ListView listaAlunos = ( ListView) findViewById(R.id.lista_alunos);


    ArrayAdapter<Aluno> adapter = new ArrayAdapter<Aluno>(this,android.R.layout.simple_list_item_1,alunos);
    listaAlunos.setAdapter(adapter);

    Button novoAluno = (Button) findViewById(R.id.novo_aluno);

Class responsible for entering and fetching students in the bank

  public AlunoDAO(Context context) {
    super(context, "Agenda",null, 1);
}

@Override
public void onCreate(SQLiteDatabase sqLiteDatabase) {
    String sql = "CREATE TABLE Alunos (_id INTEGER PRIMARY KEY, nome TEXT NOT NULL, endereco TEXT, site TEXT, nota REAL);";

    sqLiteDatabase.execSQL(sql);
}

@Override
public void onUpgrade(SQLiteDatabase sqLiteDatabase, int oldVersion, int newVersion) {
    String sql = "DROP TABLE IF EXISTS Alunos";
    sqLiteDatabase.execSQL(sql);
    onCreate(sqLiteDatabase);
}

public void insere(Aluno aluno) {
    SQLiteDatabase db = getWritableDatabase();
    ContentValues dados = new ContentValues();
    dados.put("nome",aluno.getNome());
    dados.put("endereco",aluno.getEndereco());
    dados.put("telefone",aluno.getTelefone());
    dados.put("site",aluno.getSite());
    dados.put("nota",aluno.getNota());

    db.insert("Alunos",null,dados);
}

public List<Aluno> buscaAlunos() {
    String sql = "SELECT * FROM Alunos;";
    SQLiteDatabase db = getReadableDatabase();//getReadableDatabase
    Cursor c = db.rawQuery(sql,null);

    List<Aluno> alunos = new ArrayList<Aluno>();
    while(c.moveToNext()){
        Aluno a = new Aluno();
        a.setId(c.getLong(c.getColumnIndex("id")));
        a.setNome(c.getString(c.getColumnIndex("nome")));
        a.setEndereco(c.getString(c.getColumnIndex("endereco")));
        a.setTelefone(c.getString(c.getColumnIndex("telefone")));
        a.setSite(c.getString(c.getColumnIndex("site")));
        a.setNota(c.getDouble(c.getColumnIndex("nota")));
        alunos.add(a);
    }
    c.close();
    return alunos;
}

No error is pointed out, using the debug always visualize that the array list returned by the students search is empty, the db.insert("Alunos", null, dados); I see by the debug that the completed data arrives.

I would like you to give me a light for this problem. Thanks in advance for your cooperation.