PHP include parent directory problems on Apache2

Help please
PHP include relative paths only work in the same directory and
subdirectories BUT NOT in parent directory


These are all in a folder "school" within the default htdocs folder accessed
by, for example, http://servername/school/index0.php


include0.php
index0.php
/TEST1/include1.php
/TEST1/index1.php
/TEST2/include2.php
/TEST2/index2.php

index0.php contains
<?php include "include0.php"; ?> WORKS
<?php include "TEST1/include1.php"; ?> WORKS

index1.php contains
<?php include "../include0.php"; ?> FAILS
<?php include "include1.php"; ?> WORKS
<?php include "../TEST1/include1.php"; ?> WORKS
<?php include "../TEST2/include2.php"; ?> FAILS


Is a permissions problem?