<select id="jornada" class="form-control" name="jornada" required>
            <option value="">-- SELECCIONE --</option>
            <?php
                    while ($row=mysqli_fetch_array($jornada)) {
                    echo '<option value='.$row["id"].'>'.$row["jornada"].'</option>';
                    }
                    mysqli_free_result($jornada)
             ?>
</select>

<select id="r_ruta" class="chosen-select" name="r_ruta" required>
    <option value="">-- SELECCIONE --</option>
</select>

$(document).ready(function(){
        $("#jornada").change(function(){
            $.get("get_colegios.php","jornada_id="+$("#jornada").val(), function(data){
                $("#r_ruta").html(data);
                console.log(data);
            });
        });
});