A Call for Help

I remember seeing a movie as a very young kid that struck a deep chord with me, that I've always remembered, but that I've, as an adult, been unable to find any info on. The problem is that I can't remember the title, or who was in it, or much of anything, really. Just the premise (of which I very easily could have some details wrong):

In the future the earth has become inhospitable and a group of schoolchildren (all girls?) must live on a planet where it rains all year. All except for one day, one glorious day of sunshine, that the kids look forward to all year. Some mean girls lock the main character in her room on the sunshine day and she misses it. Very tragic and very upsetting to young Tosy. After the sunny day is over, the mean girl(s) feel badly.

Anyone know what movie (TV movie?) I'm talking about??

Until Whenever