GenghisKat:
Kind of depends what you're after.
More practice? I'd advise
woodlands junior school mathszone: resources.woodlands-junior.kent.sch.uk/maths/ - just find the area of mathematics you want to work on and then search through researches/ games. Takes a bit of investigation on your part - but there's all sorts there.
Definitions for terms/ some examples:
Basic Maths Definitions: www.mathsisfun.com/basic-math-definitions.html
Maths is fun: www.mathsisfun.com/index.htm - has fairly brief, clear information on how to do things.
St Peter's CofE has some useful video tutorials on basic calculation skills here: www.stpeterssouthweald.org/tutorials/maths-ks2/ - narrators voice can grate after a while - but things are clearly explained.
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Also agree with Khan Academy (which is entirely free www.khanacademy.org/) - they've slightly changed the interface - but you can work through areas by selecting subjects/ maths/ foundation topics (=KS1/ KS2 curriculum) - you can follow US curriculum by typing in whatever grade your child is from Y4 in KS2 - e.g. 3rd grade US = Y4 UK/ 4th grade US = Y5 UK/ 5th grade US = Y6 UK). This used to be accessible from subject menu but now seems a bit hidden.
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Times table - practice to improve recall & speed - once you already know tables - Timez Attack (just download free version of game - 2 platforms - dungeon or castle): www.bigbrainz.com/ - they also have addition/ subtraction and division (inverse multiplication facts) versions as well.
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Look into what your school has subscribed your child to - Education City/ My Maths/ etc... - have games, you can learn more yourself (i.e. using Library in My Maths) and maths is ideally suited to video games. Most of the subscriptions run throughout the summer so do give them a try out of term time.
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There are a range of on-line tutorials - Khan academy as mentioned - but others are by subscription: Komodo Maths/ Mathletics/ Maths Whizz/ Mathsfactor. Various of us have sung praises of these - my view is try them out (all have free trials) and see which suits your child. We opted for this - but only once we hit that point of complete despair - struggling child/ school unwilling to help and refusing to recommend workbooks/ suggest websites and we personally couldn't bear the fact that our 7 year old couldn't even take 1 from 10. I've posted a lot about what we did and why here on MN - but basically if you hit that wall - there are solutions out there - just do some research and include your child in the decisions (as it will never work if he/ she doesn't like the computer programme/ format).
HTH