Hi there.
IEP (IBP) should be something you agree with ...so your imput is required..........Please do question what the goals are trying to address, what the school are going to do to support DC developing the skill to meet the goals, and how they will measure success (they should be developing SMART goals - Specific, measurable, attainable , realistic, timely).
You many want to help them define appropriate goals that meet his needs more specifically which would also include what they will be making note of to record success/progress/, how that is going to be organsied and managed in the classroom, make sure its something that can actually be done in the classroom and something DC can achieve, and give reasonable expectations ( how many times will he 'get it right' 50%, 80% of the time?) and reasonable time to achieve the goal.
If you feel there is something in the IBP that simply cannot be met because its either impossible to measure, or just too unrealistic, then say so.
Tried and failed strategies should be challenged (the new teacher may not realise this is the case), as should the assertion that DC is choosing not to behave as desired.......... no-one 'chooses' to be in trouble all the time. What justification do they have to assert that?
If DC fidgets, can he be given something to fidget with that stops the wider disruption?? This is what is done to support my DC to go to assembly, with his fidget toy (something that he can twist and pull and tie up) he will sit quite happily and quietly with the class for the 20-30 minutes required causing no disruption what-so- ever (and despite the distraction for himself he IS listening)...without it he is poking other children, taking his shoes off and playing with them, turning round, talking, laying down, and worst of all breaking into song (on the one hand hilarious as its usually something very inapproriate like Lady Gaga, by terribly unwelcome and very diruptive)
You might assume that the SENCO and teachers would have lots of experience at doing these things and should be instructing you on how they work..........dont assume anything, you need to use your own resources to make this the best it can be for your DC (what do you do at home for example, what actually works??)...question everything (in a supportive way).
Expect to give lots of input, push back on what is suggested if needed, offer alternative solutions if you can, and then make sure they are actually doing what has been agreed (the next stage of frustration in many cases).
Good Luck!