siobhanm1
DDs both use My Maths - and also have come across this problem - struggling on a homework but the next homework is slightly different and they make different mistakes.
I agree with Noble - what may help after getting a yellow or red smiley face instead of green - is to review the lesson again.
I'd also add - that with the more complicated problems (I too remember the CD in the crate problem) - encouraging them to do it on paper and check their answer helps.
I think in part this is going to depend on your own maths skills as a parent - if you are confident with the calculations your DD is being asked to do - one solution may be to check her answers before she uploads them - pointing out any errors.
Having said all of that - I agree with many here that have suggested this approach to homework is not helpful. Homework is an opportunity to learn/ extend understanding/ consolidate & revise - but very definitely shouldn't be about getting things 'perfect' or 'near perfect'. Sure that should be a goal - but part of the overall effort - working at it should also be rewarded/ recognised.
So I would advise writing/ e-mailing the teacher, explaining that your DD has repeatedly attempted the homework assigned (15 times) but is clearly struggling with the concept. Although you respect that she has failed to achieve the green smiley face on My Maths and therefore merits a detention, you wonder if it might not be more productive if the teacher or a fellow student could work with your DD on this homework and help her to understand what she is getting wrong - as clearly there is a consistent problem with this concept.
Personally I think this is a mis-use of technology. The teacher will have the metrics from My Maths to see how long and how often your DD worked on these homeworks. She will also know how well your DD did on the questions - e.g. 59% correct, etc... So she should be more than aware that your DD has repeatedly tried this and is struggling. One would presume that good pedagogy from a professional educator at this point would be to intervene where the pupil is struggling and immediately address whatever learning issue there is. I wouldn't put it that bluntly - but I would suggest that this is the point where the teacher or a maths support group should be intervening to help your DD.
Now these may exist at your school (as they do at our school) and the issue may be that having been given a week and the teacher knowing that she's available to assist and their are maths clinics open & available at breaks/ lunch/ after school on several days a week (as at our school) - a child struggling with something need only come along and get help. And indeed this may be the point of the punishment - teaching her to be more proactive and ask the teacher/ go along to maths clinics for help with extended assignments like this (as you said she had a week to achieve green smiley face on this concept). I'm not saying this was the logic - but I think you shouldn't presume that the school didn't have things in place (help at breaks/ lunch/ after school) which your DD for whatever reason opted not to take advantage of - after all she was getting instant results and could see it wasn't going well - so she also was fully aware something was amiss and she was struggling on this concept.
HTH