FruitCakey:
Without going into huge detail - but starting with the proviso that for us we had some pretty grave concerns about the quality of education at DDs primary school what we did:
Reading: bought/ borrowed/ traded books and ensured ~30 minutes a night reading KS1/ KS2 lower. KS2 upper girls moved on to reading on their own - but I would listen to them read 1 or 2 times a week (depending on how hectic things were).
Writing: I'm evil - I make them write thank you cards for every present. I also am big on having them send postcards to friends/ family when on vacation. Of course they must write Father Christmas - explaining whether they've been good or not.
DD2 really struggled picking up cursive - so we got some Collins handwriting workbooks and she worked through these (often in front of the tv) at her own speed.
Maths: This really was an issue for DD1 who finished NC L1 in KS1 SATs and was barely able to take 1 from 10 by end Y2. We opted for an on-line maths tutorial late Y2 - steadily putting in between 1 hour to an hour 1/2 over 5 installments across a week between late Y2 - end Y6. DD1 adores computers/ video games - so never really viewed this as learning - although sometimes she did find it tricky.
DD2 got jealous of her sister doing this 'fun maths'- so she joined as well - basically because she thinks it's fun.
For us - the issue was that core concepts and appreciation of number patterns was clearly not sinking in with DD1. (I'm not saying it wasn't taught - but for whatever reason it wasn't being retained by DD1). She just didn't have any calculation skills to speak of by the end of KS1 and was utterly hopelessly confused between when to 'estimate' and when to actually all out add. We actually had a major row about whether 2 + 2 was 5 or not - she said her teachers told her it was right.
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Geeky things we do anyway that children get dragged along for:
audio books on long car journeys
visiting museums
visiting gardens
visiting historic houses
going to plays
going to concerts
going on holiday (and doing a lot of the above)
watching documentaries/ Sky at Night/ Spring Watch/ etc...
watching Royal Institute Christmas lectures
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Overall I'd say the girls probably put in about 45 minutes to 1 hour a day, 6 days a week on 'extras'. Not done all in one block - and often broken up into 15 minutes (after school writing/ on-line maths), 15 minutes during sister's bath reading to me or DH, 15 minutes+ us reading to them or them reading to themselves before bed.
Writing (thank you cards/ letters to competitions/ etc....) usually happens at the weekend and often takes place whilst we're cleaning/ cooking. DDs both keep diaries and also write little stories in special notebooks I buy them - tend to do this if phases (lots of activity and then maybe nothing for a few weeks).
It sounds like a huge amount - but split up into 3 blocks of 15/ 20 minutes - and done in a relaxed way as part of normal day to day routine - it really wasn't that noticeable. There was still tons of time to play with friends, go to clubs/ lessons, bake, slouch in front of the tv, play video games, etc....