To be really honest the differences theologically
between eastern orthodox Christianity and Catholicism are small.They focus around the eucharist and where ecclesiastical authority should be.That is why you can take communion in an orthodox church if you are Catholic.They are theologically closely aligned.
In brief, orthodox Christians do not look to Rome for direction and believe something slightly different about the eucharist.
The reason I mention this, is that a young child cannot possibly have a handle on these differences and therefore any conversion wish will be seen as being tied to social and educational pressures and will not further your cause.In fact they may take a dim view of someone converting for the wrong reasons.
I would just talk to the secondary school and ask if any year has an intake of non catholics.If it is a good school, I suspect probably the answer will be no.Sorry