Hi summerplease:
I wouldn't worry about what the school is ticking off or not in terms of observing 3 separate secure attempts at whatever target (adding a negative number to a positive number, making a word an adverb or adjective by changing the ending, using WOW words, etc....). To be honest our school claims to be doing this and every parent/ teacher meeting for the last 2 years (once a term) the list is in fact a photocopied blank list and nothing is put to paper. We've even been told for DD1 that at the start of the school year any existing observations from previous school year are 'rolled back' - so they start observing 3 achievements of activity from scratch again.
I have found the whole they're not noticing where my kids are at (and we have both extremes: DD1 hugely behind and DD2 way ahead). That the solution is to just blithely ignore the school - there is real freedom in just viewing school as day care. You basically can never be disappointed.
Now I presume if your school hasn't taught negative numbers yet - then your DS must be learning about these things in some other way - on-line games, on-line tutorials, actual tutorials, workbooks, etc.... So you are doing more at home.
I think you have to play the long game. At first the school may not pick up on it - or like our school you may be scolded as a parent for "doing too much at home". But if your targets seem reasonable and achievable to you (be they ensuring your child can add, subtract, multiply & divide or read books for chronological age by end of KS2, etc... - and these are our targets, well ahead of our school's goals) then my feeling is just do your own thing and ignore the school.
At the end of the day the KS2 SATs (which are independently moderated) will be a determiner (for streaming on entry to senior school) and from what many are posting here in Y7 most schools re-test pupils anyway, to establish where they're at by their own standards.
Finally, if you're preparing for the 11+ - in our area at least - the school feels absolutely no obligation to support or assist a child in that endeavor. That being the case, you do simply have to be tough about this and proceed as you think best - because this is certainly an area where school to home communication/ support is non-existent.
HTH