FiveHoursSleep:
I agree with you that it could be she's a bit bored with school, but you did say...Now she's encountering stuff where she has to think, it's like she can't be bothered.
I've found that when school work suddenly gets a bit tricky and possibly isn't that well explained in class, this can be the point where pupils lose heart/ zone out/ give up.
My advice is play to her interests:
If she's interested in math and enjoys playing video games well why not encourage her to play video games that support her current maths issue (maybe learning times tables right now - which is typical for Y3).
My first port of call would be Woodlands Junior Maths Zone: resources.woodlands-junior.kent.sch.uk/maths/ - all sorts of resources for multiplication under TIMES TABLES.
Once your child has the idea of times tables but maybe finds a few tricky to recall consider games that work on speed of recall (again these are all free):
times table games on math champs: www.mathschamps.co.uk/#home - you'll have to explore because they're spread out over the age ranges (5-7/ 7-9/ 9-11) - but this is helpful because it is arranged in the logical order to learn tables.
multiplication dot com: www.multiplication.com/games
lots of different formats - let your child have an explore and try out different games - they're bound to find one they like.
Timez Attack: download the free two platform version
The game will test your child and start off from where they're at. You child can be a small boy or girl ogre and races through a dungeon or castle solving multiplication problems which are shown as traditional vertical problems that you type the answer into and also and multiple additions (so with 6 x 8 - you would count up 8/ 16/ 24/ 32/ 40/ 48 - by throwing snails against a wall - very odd I know but it works). Link here: www.bigbrainz.com/
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For science more and more really cool websites are starting to appear:
MIT (Massachusetts Institute of Technology) and Khan academy K - 12 (US Kindergarten = YR through 12th Grade = upper sixth form): www.khanacademy.org/partner-content/mit-k12
Science Sparks: www.science-sparks.com/
Science Bob: www.sciencebob.com/blog/
Also look out for things like the Royal Institution Christmas lectures (shown on BBC): www.bbc.co.uk/programmes/b00pmbqq/episodes/guide
or www.rigb.org/christmas-lectures - they have links to past lectures.
Peter Worthers 2012 lectures on chemistry with great experiments really captivated my kids.
In 2012 & 2013 the RI ran an advent calendar (2012 - favourite elements from the periodic table with a different speaker for each element - often comedians & 2013 - was about chromosomes). So be sure to look out for the 2014 advent calendar.
Also advice TV shows like Spring Watch/ Autumn Watch, The Sky at Night (new revamp and much more children friendly), Stargazing live, documentaries - the recent BBC four offerings on bones (The secret of bones www.bbc.co.uk/programmes/b03vrtkp or fossils (Fossil Wonderland www.bbc.co.uk/programmes/b03y6tg6) have been fantastic.
and of course don't forget to see things like Science Museums, engineering museums, etc to see & learn more about science/ maths.
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My advice is school is not reaching her/ keeping her engaged then doing a bit of exploring at home and trying to foster her interests will make a difference and help to keep her motivated as a student.
HTH