Summer Term is one of those that has you rolling your eyes from beginning to end. Luckily I also only paid 20p in a charity shop. 
Starts off with Erica naturally recognising Joey from over the road in London (I think it's London anyway) and dashing over to introduce herself as "hello, you've never heard of me, but you did vaguely know my parents and you're now my legal guardian." Can any of the famous authors tell me: Is this a frequent happening to them?
Of course Joey is so wholesale and motherly she promptly agrees and takes Erica back. On train.
Naturally that can't be without incident having Joey on board, so it crashes. A random baby is found, who only speak French (and I think only one phrase "moi, J'ai Marie Claire" or something). Erica rather likes the baby and Joey can't resist being even more wholesale so she insists on taking the baby, particularly after she's met the dad and doesn't like him. Well actually you can see the dad could have been the pope and she'd have disliked him and thought he isn't suitable, because she wants the baby so everyone can exclaim at her wonderful mothering skills. Clearest case of kidnapping trying to keep within the law I've seen.
So she pinches Marie Claire, and promptly forgets about her until the end of the series. Obviously she was much better with them than her dad who only had her to care for 
Reminds me a little of the Robin.
Then we have hints Erica is struggling to settle down, but no evidence of it. Hints that things are going to get worse, but they don't really.
And the usual Chalet School incidents, like the thunderbolt hitting the cricket pitch and setting it on fine, as is a frequent problem at that school. NAturally to stop it they have to dig an olympic sized swimming pool out of the cricket pitch, which allows for two things:
- The prefects to mourne their cricket pitch.
and 2. Erica to fall down the whole for a dramatic rescue. Obviously if you don't have a handy cliff to drop a few pupils off, you create your own.
We also have the jealous schoolmate of Erica's, who obviously steps into the breech when needed and makes up after that. The incident? Obviously when someone spills perfume down themselves you need to be acreful of swarms of bees, because then the bees decide they love Erica and swarm onto her skirt. I suggest they don't use this for attracting bees really, because I'd be very surprised it it works.
And if her arch-enemy is anything like most girls of that age, they would have all fled at 2 bees let alone a swarm.
And don't we have the Gretchen imitating Joey's Green incident (only not with green). But dying pupils from top to bottom is quite a placid activity for the Chalet School.
And all ends happily with Erica deciding she's a real Chalet School girl.
I think there is some suspicion that EBD didn't actually write this (or prefects). And it does slightly read as though someone has written down lots of incidents and someone else has tried to join them together to make a book. Or perhaps all the incidents EBD had meant for the next dozen books, had to be condensed into one so she could get them all in.