Hi expansivegirth:
There are plenty of non-web-based books - CGP does a lovely series with good explanation of methods, but my advice is to go along to a big newsagents or book store and have a browse with your DC there as well, because between you - you'll know what is the most interesting format (lots of pictures, lots of sums to solve, little reading, lots of written explanation, etc....). So it isn't just about finding any old workbook - it also is about finding a workbook that makes things clear for your child to easily understand the underlying concepts involved in whatever calculation method you're working on.
Personally, I wouldn't write-off some of the on-line systems. At the end of Y2, DD1 could not even take 1 from 10. She simply did not understand subtraction at all and somewhere along the line got estimation (so guessing that 5 - 3 should be around 2) wrong (she'd guess 3) and unfortunately she said that this would be marked as a correct estimation by her teachers, because it was within 1 of the correct answer. Maths was a nightmare in our home - I was seriously worried, she hated it and was convinced she wasn't very good at it. We were also at a school where there was no homework to speak of (just colouring in patterns for maths) and the teachers were unwilling to recommend workbooks, so I was left to it.
We went over the mathsfactor. It's web-based but its mixture of video (Carol Vorderman presenting) explanation, practice games, timed warm ups and straightforward sums to practice is a no nonesense, slow and steady, building block approach that has (in our case at least) resulted in a child who has strong calculations skills and a thorough understanding of number pattern. Please have a look: www.themathsfactor.com/. If you don't want to go the route of joining, can I suggest investing in their worksheets for now and/or possibly joining the summer school in late spring. It's a one-off payment of about £20 for the summer school and it may well help your DC make up lost ground. (and I stress I'm just a Mum - but am thrilled with this programme which has solved so many of our problems with learning addition/ subtraction/ multiplication and division).
Although I absolutely understand your search for workbooks (I started there too) - the on-line format makes practice seem like playing a game, the visual presentation means that numbers aren't something for just in your head and somehow the clear presentation (verbal and visual) with practice just seems to crack through those 'mental blocks'. It starts off by testing your child where they're at and goes from there. We've committed to an hour a week (roughly 5 practices a week for about 20 minutes each) since late Y2 and DD1 is now flying in Y5. She can do it on her own now (when they're 8 and under, you may have to help type in answers) and basically I can get on with cooking, cleaning, helping DD2 with her work, etc... whilst she's doing a lesson. I know it's good quality, she enjoys it and the time commitment is fairly minimal - usually around 20 minutes a lesson (video, warm-up or game and exercises on that concept).
Other parents have praised maths whizz (www.whizz.com/) and mathletics (www.mathletics.co.uk/) here on mumsnet. All of these have demonstration videos you can see and offer free trials.
Free on-line sites that have also helped for particular stumbling blocks include:
Woodland Junior School Mathszone: resources.woodlands-junior.kent.sch.uk/maths/
Cool Maths Games: www.coolmath-games.com/
Crickweb KS1 Numeracy: www.crickweb.co.uk/ks1numeracy.html
Ambleside mathszone: www.amblesideprimaryschool.co.uk/Learning-Zone/Maths-Zone.html - just click the calculation skill you want practice in and select the most appropriate game.
Oxford Owl has a maths section for early years and KS1. There are some very straightforward addition/ subtraction games to 20, adding roll of two dice and early multiplication games here: www.oxfordowl.co.uk/maths/fun-activities/5-7/
Mumsnet has some free games: www.mumsnet.com/learning/learning-zone/learning-zone-introduction and we've found some of the games on the Pearson Mathschamp site really good www.mathschamps.co.uk/#home and its set up by age groups (5-7/ 7-9/ 9-11). The Mumsnet shop also has informatoin on Carol Vorderman's maths made easy workbooks - link here: shop.pearsonforparents.co.uk/5-7/EnglishMathsWorkbooks/EnglishMathsWorkbooks.aspx
I've so been there Expansivegirth. I felt overwhelmed by all the choices and desperate to help my DD1 catch up. But take a deep breath, there is time, you've caught the problem early and give yourself a few months to try out various things and see what works best for your child (because we're all different and we each respond better to some methods than others). However, don't underestimate the huge difference in today's children and us oldies - they live in an age where learning on computer is preferable to old fashioned books/ paper and pencil. They genuinely are more interested in learning in that highly visual format and if done well, it means you simply have to provide the computer, possibly a snack, a bit of typing support if they're very young, and off they go and you're free to get on with what you need to do (which may include sitting there and supporting them, but can mean you're free to do other things in the knowledge they're getting the help and practice they need).
HTH