FairyPenguin:
I think your DD is approaching this well - knowing to double 2x table facts to get 4x table facts (4 x 9 example) - shows appreciation of patterns/ numbers.
The issue is speed. I see why you're questioning the need for speed - but let's just start with how you might improve speed....
We found that the stage between being able to work out the answer and being able to answer swiftly just basically required a lot of practice.
Our solution was to play a lot of different video games.
If your school belongs to My Maths - snaky sums is fun and great practice.
You can download the free version (2 platforms - castle/ dungeon) of times attack: www.bigbrainz.com/ - you're cast as a young ogre who goes through the castle or dungeon solving multiplication problems. These are also shown as multiple additions. You then are quizzed by progressively fiercer & bigger ogres. The stress of the big ogre quizzes is the really useful thing (although it made DD2 shreak when they came out to quiz her) - because it's forcing you to think under pressure.
Woodlands Junior School Maths Zones has lots of resources/ games to help with practising times tables: resources.woodlands-junior.kent.sch.uk/maths/timestable/index.html - lots of other great resources in maths zone as well.
Multiplication dot com - has great games to reinforce times table fact speed: www.multiplication.com/
Finally - you can reinvent card & board games to work on times tables.
You can play snakes & ladders (may have to play the board more than once) - practicing multiples - so maybe you need to work on x6 table - get two dice - and you move that roll's multiple of 4 (so if you roll 9 you move 9 x 4 = 36 spaces). We found with numbers >5 you had to play the board at least 2x. But with two dice you have up to x12.
You can play SNAP with an ordinary deck of cards. Ace = 1, 2 - 9 as marked, Jack = 10/ Queen = 11/ King = 12. Decide the times table you want to practice - maybe x3. Shuffle cards and place them in a pile face down. I usually make a post-it and wirte x3 (or whatever table - just to remind us all what we're doing). Flip the card. Say it's 9. The first to shout 27 - wins the card. The winnder is the one with most cards at the end.
With MULTIPICATION SNAP - we started off letting DDs do well at first and then gradually got fiercer about answering quickly. This can get very loud and rowdy - so (based of bitter experience) - may not be wise to play out at a restaurant whilst waiting for your food.
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I think in terms of why is the school trying to push this - why do you need speedy recall of times table facts - that's a slightly more complex answer.
Yes - of course knowing your times tables is the main issue - but what they're actually after is near instant recall of times table facts. Knowing them so well it takes you only milliseconds to know 12 x 12 is 144 or 9 x 8 = 72.
This is important when ultimately you're presented with 5781 divided by 3 will be a whole number (so knowing all the digits in 5781 add up to 21 which is divisible by 3) - knowing quick multiples/ working out that 3 goes into 5 once, remainder 2 & draw down the 7 to get 27 - 3 goes into 27 9 times, draw down the 8 - 3 goes into 8 2 times - remainder 2 draw down the 1 - three goes into 21 - 7 times - so your answer is 1393 (long division way).
or to use your own knowledge of x3 table to work it out in chunks.
5781 divided by 3
knowing 3 x 1000 = 3000
3 x 900 = 2700
3 x 20 = 60
2 x 7 = 21
3000 + 2700 + 60 + 21 = 5781
so adding those multiples up (1000 + 900 + 60 + 21) gives you 3 can go into 5781 some 1981 times.
And ultimately - it is speed (facility) of recall that allows you to then go on to really fly with more complicated forms of mathematics: algebra, trigonometry, calculus. Just dealing with fractions or percentages is so much easier if you have strong times table skills. Too many politicians/ academics play fast and loose with statistics purposely to confuse/ obfiscate the issue. Certainly many people just don't get that buying something on credit often means you're paying for it 2x or 3x over. Now - you may have needed the item/ house then and there and this was the only way to access to capital to have it - but a lot of times you don't really need that sofa - understanding saving for a bit longer and buying it cash saves you money in the long run is in your interest.
You need that level of maths skills for many sciences - chemistry (calculating temperatures/ properties - graphing results, etc....)/ physics - calculating speed, orbits (ellipses/ circles), arcs, pressure (gravity), half-lives, etc..../ biological studies (for example calculating statistics/ percentages/ proportions/ etc...)
I think it's very easy to dismiss learning times tables as not particularly improtant - but really having a solid grasp of times table facts and being able to apply that knowledge in multiplication/ division swiftly is a real advantage going forward: e.g. www.greatmathsteachingideas.com/2014/01/05/youve-never-seen-the-gcse-maths-curriculum-like-this-before/
So yes, FairyPenguin - I get that you feel your child knows the concept (and I think you're correct there) - but I think you need to think through the advantages of near immediate recall of these facts can be hugely beneficial in the longer term.
HTH