We have a couple of pretty successful activities at my school. We have Breakfast Under the Stars, which along with being a pancake fundraiser for the 8th grade is a science night. We invite a "mad scientist" or the "grossology" presentations along with an educator from an animal shelter and some star gazing activities, among others. It has been a great success the last two years.
We also did the "math-a-phobia Hotline" play last year, which was wonderful! It is a math related play, all prerecorded that we simply have the teachers act out and lip synch to. Each scene has a math problem that goes with it, that the audience figures out. It is fun and funny and the kids and parents really enjoy it.
Last but not least, our school has monthly family literacy night. The activities vary, but we almost always have a guest speaker talking about their career, every child gets to take home a book and we raffle off some extra interesting books (like a Guinness Book of World Records or something). Sometimes students from our school preform or do readings. Sometimes they do science experiments with their parents! Students also get points toward our library's end of the year auction by attending and many teacher also give homework passes to encourage attendance.
Check out our school website: www.discoveryacademy.org.
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I take it you are referring to an activity that a child can do with their parents. You might like to think about applying such disciplines to everyday contexts. Getting students for example to help draw up a budget for their family's weekly shop might be a good place to start. This would include reading and math, and could even be extended to include science if students can count calories and salt content of foods. Hope this idea helps!