Aluno com ID 1 não aparece na lista.

Bom dia, Aluno com o ID 1 não aparece na lista. Ou seja, algum problema na configuração do layout xml. Outra coisa, No projeto tem dois arquivos de layout xml, o primeiro que é content_lista_alunos.xml e activity_lista_alunos.xml. Qual deles devo modificar, sendo que o botao de adicionar tá configurado no activity_lista_alunos.xml, com qual devo trabalhar? Se eu remover a parte do codigo do toobar acaba removendo o a barra do aplicativo. Segue o codigo dos dois xml:

activity_lista_alunos.xml

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".ListaAlunosActivity">

    <Button
        android:id="@+id/novo_aluno"
        android:layout_width="56dp"
        android:layout_height="56dp"
        android:text="+"
        android:textSize="40sp"
        android:textColor="#ffffff"
        android:layout_alignParentRight="true"
        android:layout_alignParentBottom="true"
        android:layout_marginRight="16dp"
        android:layout_marginBottom="16dp"
        android:background="@drawable/fundo"
        android:elevation="6dp"
        android:stateListAnimator="@null"/>

    <android.support.design.widget.AppBarLayout
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:theme="@style/AppTheme.AppBarOverlay">

        <android.support.v7.widget.Toolbar
            android:id="@+id/toolbar"
            android:layout_width="match_parent"
            android:layout_height="?attr/actionBarSize"
            android:background="?attr/colorPrimary"
            app:popupTheme="@style/AppTheme.PopupOverlay" />

    </android.support.design.widget.AppBarLayout>

    <include layout="@layout/content_lista_alunos"/>


    <!--<android.support.design.widget.FloatingActionButton-->
        <!--android:id="@+id/fab"-->
        <!--android:layout_width="wrap_content"-->
        <!--android:layout_height="wrap_content"-->
        <!--android:layout_gravity="bottom|end"-->
        <!--android:layout_margin="@dimen/fab_margin"-->
        <!--app:srcCompat="@android:drawable/ic_dialog_email" />-->

</RelativeLayout>

content_lista_alunos.xml:

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    app:layout_behavior="@string/appbar_scrolling_view_behavior"
    tools:context=".ListaAlunosActivity"
    tools:showIn="@layout/activity_lista_alunos"
    android:orientation="vertical">

    <ListView
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:id="@+id/lista_alunos"
        android:layout_below="@+id/appBarLayout"
        android:layout_centerHorizontal="true"/>

</LinearLayout>