The teacher gave me the report in class in the morning, and I handed it to him in the car on the drive home. He cried. He is a high achiever and his teachers said it just might be the little jolt he needs. They told me they would speak to him today about his report but he said they didn't mention anything about his maths group (they said to me that they would ask him what group he'd like to be in, just to see if it makes him realize he may have to go down a level in the maths groups). I had wrongly assumed that everything was going along fine - he has been rushing his homework through to hand it in early, and some weeks I really didn't see it because he would say he'd already handed it in (say, Tues or Wed) for marking and that it was "easy". When I read through his homework book this week, I could see he had quite a few careless errors.
I told him that after the holidays, I needed to check through every week of homework, and I have also bought one of those Naplan maths books (from Big W) for him to do a little extra every week. Hopefully I'll be able to better monitor how he's going. The teachers didn't actually suggest I do anything for either him, or his year one sister. I'm in two minds about it because I don't think childhood is all about school work, but I am mindful that if they miss out on things early on, it will impact their later years in school.
Quite a few who have commented have suggested that a C is actually pretty reasonable, considering the new curriculum, but after seeing that some of his other classmates were still getting B's and A's for the same subjects, I'm not really happy to accept a C. I think he can do better, and I do hope that next term things improve. I was actually quite upset yesterday, and was trying to work out what is best for all of my children - I don't think the school they're at now is responsible, but am trying to determine whether the private school may be a better option, anyway.
Thanks for all the advice, it's great to hear what others have experienced and very helpful.
Just edited to add that my other son, year 6, did very well, receiving A for english, B for Maths - what he has done every other year. So he's done well despite everything stepping up a notch. Which is a little confusing.