Lonecat:
From what I'm hearing here it sounds like there's 3 problems:
- frustration/ lack of confidence negatively affecting her work
- processing speed issues (possibly with basic multiplication facts)
- application of calculation skills to word problems
The last is actually pretty classic of a child who 'gets it' when it's very formulaic - today we're doing two digits x 3 digits - and all the problems (which probably are only a handful and straightforward) are presented in the same way - no surprises/ complications.
I don't think I would worry about a 3% drop between Y4 and Y5 on a test (presumably L3 - L5 old KS2 SATs paper) - as some tests are harder than others and some days are better than others for children.
Can I just ask - what is the homework from the school like. Does she actually get homeworks which stretch her in the areas she's struggling - so word problems where she has to work out percentages/ averages/ etc...? Or is it more a case of the entire class gets an identical sheet of problems to solve - often bearing no relation to what has been going on in class?
My advice is this:
put some time in on multiplication fact speed - so that recall of a fact (either multiplication or division - i.e. inverse multiplication fact like 36 divided by 3 is 12/ divided by 4 is 9/ divided by 6 is 6. (multiplication.com has tons of games - or download the free version of Timez Attack www.bigbrainz.com/ which has you solving times table problems under a bit of stress in quizzes by ogres).
I do find that teaching of fractions/ percentages/ proportions/ ratios in schools can be very shaky - this is about the point most primary teachers can lose the plot. Again - doing work with this so that she starts to see that 1/4 is the same thing as one out of 4 students or 1:4 ratio or 25% - and can easily switch between them will be a huge help.
Now there are several solutions - and I see that above someone has already discussed doing more through Education City.
If your school subscribes to My Maths - sign in and select homework - you should see NC Levels and little bars indicating what % of homeworks in that level have bee assigned. Based on that you can work out whether the teacher is assigning NC L3/ L4/ L5/ etc... homeworks.
Select that level - and then select the unfinished homeworks in that level. You will get a list of various homeworks and can target things like percentages/ fractions/ proportions/ conversions (i.e. converting £ to USD$)/ ratios/ etc.... The lessons will review the technique of dealing with such problems and the homework will give useful practice.
My Maths also has a lot of games that can also help you work these skills.
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The Woodlands Junior School Maths Zone has links to all sorts of games and resources to support a wide range of calculation skills: resources.woodlands-junior.kent.sch.uk/maths/ - just select the area you want to practice and go for it.
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Khan Academy (which is entirely free) - has video explanation of various calculations - and this can be useful when reviewing techniques - especially if there has been a disagreement (often because 'in school' primary maths terminology differs from 'traditional' terminology or HE Mathematics terminology. www.khanacademy.org/ - just select subjects/ maths/ and then use search engine or select the area under FOUNDATION (which is for primary grades).
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If you feel that the issue is that she's starting to really struggle/ not getting how to apply basic calculation skills to 'real life' problems/ more complicated word problems/ etc.... - there are a wide range of KS2 SATs/ 11+ workbooks that have these types of problems or you can consider subscribing to an on-line Maths. I get that she's resistant - it's getting hard and she doesn't like struggling (a rare occurrence in most pupil's lives in primary schools in England) - but encourage her to see these as puzzles and 'just for fun' rather than you being unfair/ cruel.
There also are a number of on-line maths tutorials available by subscription: komodo maths/ maths whizz/ mathletics/ mathsfactor - all of which have been praised by various of us (myself included) at some point or another here on MN. Sometimes the old fashioned solution of a bit more practice & reviewing methods is the answer. For us it certainly worked. All of these offer free trials - and if you do go down this road I'd seriously suggest you include your DC in the decision of which programme to try - because they're all different and the various options appeal more to some than others.
HTH