Is it only your child, feel this way ?
How about the rest of the students, inside his IB class ? How do they feel, about this same Teacher ?
If is the general consensus of the whole class that this IB Teacher is really no good,
then,
Let the students inside his class raise this issue up, directly to the Form Teacher plus the (Academic VP + Principal), inside ACSI. Let the students themselves, at 18 years old already, raise this issue up, themselves, directly to the VP + Principal. Parents should not intervene anymore, when students have already reached this age (18 years old).
What happen next is,
if what the students collaboratively as a class, feel that this IB Teacher (ACSI) is really no good, then,
ACSI should, ought to find another Teacher, to substitute and to replace this no-good IB Teacher. Of course, ACSI (P + VP) will ask their students :- in what way, is this IB Teacher, no good ? Show evidence.
They can inform this Teacher to teach, up to the remaining balance days, in the current Term. When the next new Term come, ACSI ought to have replaced this IB Teacher, with another one. This no good Teacher, would have left the school, in the next new Term, if he or she, is really no good.