I think years 3 and 4 are like our US grades 3 and 4–is it mostly 8-9 year olds?
I have taught multiple grades before, and understand your struggles. However, I think in the long run, Daily 5 and CAFE make that easier. Are you using CAFE as well as Daily 5? (I have to admit I’m not so knowledgeable about Math Daily 3.)
I first would look for all the similarities between the topics (which I think would compare to our Common Core or state standards). There probably are more similarities than you may have thought. We did a comparison between our first and second grades a couple of years ago (6 and 7 year olds), and were pleasantly surprised at the number of similar expectations–the big difference mostly was in the “sophistication” of the expectation.
So, perhaps, your mini-lessons could be based on those similar expectations. Then when you meet with strategy groups, it may turn out that you have some Yr 3’s and Yr 4’s in the same groups–again, checking the expectation of mastery of goals.
I think this might be a good place to start. Have you joined the Facebook group from Australia, Daily 5 SA? Here is a link: https://www.facebook.com/groups/479471055422384/
You have to ask to me a member, but everyone is accepted I think–even me in Texas, USA!! I read some very interesting topics there, and some folks have done amazing work to match the Australian expectations with Daily 5/CAFE. Perhaps some of those folks can give you better advise than me, since I’m not so familiar with your system.
However, I hope you will share back about what you’ve tried. It will help us all grow in our knowledge of how to make it all work!