I hate this 'go straight to the head' nonesence.
first, if you have a problem with somebody, you should at least have the courtesy and the guts to speak to that person directly.
Only if you are still dissatisfied should you seek to take it further.
In any other situation you would initially try to speak to the person with whom you have a problem. As if the head should directly deal with every single problem of every single child/parent in the school.
Not to mention of course the possibility that wires have been crossed/there's a misunderstanding of some sort or a rational explanation.
Just to be clear though OP; no way should the teacher be chucking dc work in bin like that. But you need to find out, through a calm conversation with the teacher directly, if this is the case. Ideally also make an appt, rather than just turn up, esp at a busy time.
When my ds started at a new school, he was being made to re write pages of stuff. We moved countries, so he was in effect 1.5 years behind his new peers. He was in the 1st class in his old school, and hadn't even been taught to write yet, then moved in basically a 3rd year class where all the kids were writing cursive with fountain pens. I found out, went in, explained and said I didn't want him re-writitng anything. teacher on board, hadn't realised the situation (lack of communication), all sorted with no upset and no blazing guns.