47: The New Chalet School: Elinor M Brent-Dyer: ISBN 0 00 691018 1
48: A United Chalet School: Elinor M Brent-Dyer: ISBN 0-00-692931-1
These two tell of the closing of the rival St Scholastika's on the other side of the lake, with the two sets of pupils being united in the Chalet School. They're fairly lighthearted, and much in the same vein as earlier books. Though in this case the mischief is being mostly caused by children outside the school, rather than those in it.
49: The Chalet School in Exile
50: The Chalet School at War
51: The Highland Twins at the Chalet School.
The first of these tells of events when Austria is drawn into Hitler's power, and how some of the Chalet School pupils are forced to flee into Switzerland after standing up to Nazism. The whole school soon relocates to the Channel Islands where it hopes to be able to continue in greater safety. In the second it has become clear that even here is not safe, and the school moves again to the Welsh border, where both the last two are set. Being set in wartime somehow seems to make these last 3 have a bit more depth than some of the others, though there are still the usual schoolgirl tricks going on. And of course we see how Joey and Madge's lives are growing and changing too, as well as seeing some of the other old girls.