Favouritism goes on in many schools, state and private.
Same couple of favoured children front and centre in the class photo three years running for us. Another child of a parent heavily involved in PTA is regularly chosen for tasks/roles that are an honour.
One child finds the academic work very easy, excels and gets singled out for praise over and over again in assemblies. This child verbally bullies my oldest child and I have mentioned incidences (that have caused tears at bedtime when we talk about the day) to the class teacher who said "it must be happening when it can't be seen by anyone else because no-one else has noticed anything".
I made a donation to fund materials for a specific class project and lo and behold my child was specifically praised in assembly that week for his work on the project. Suspicious, me, I sure am ?
I tolerate the situation because in a way, rather sadly, it reflects real life and I don't want my children cosseted too much in their small primary school. I do however offer reassurance to my oldest child and we will have a new teacher in September who may be less biased.
As for doctoring the SAT results. My oldest child's attainment levels have been understated for 2 years running now. They bring home and are working their way through reading books for an 11 year old but their documented reading age is apparently that of an 8 year old. (I have been made aware by my SIL who is also a teacher that this means the school will officially be able to show that my child is making progress each year under the schools guidance/teaching, even if progress stalls for some reason later on, so boxes ticked, school performing well, etc etc).
If you can't move schools, could you let your kids joind a drama or sports group where merit is based on actual achievement so they can see a different way. Can you protect them from the effect by joking about who will be front and centre at each performance or are they too yooung for that ?
Can you ask for regular meetings with the class teacher over your child's progress in class. Money talks, it's true, but there is also the fact that where it is known that you are proactively taking an interest in your childs' progress, the teacher would be wise to give your child enough attention too. Sometimes, he who shouts loudest...and all that.