It's quite common for noble families to send children to some of the larger temples for an education, but being directly fostered means very little emphasis on rank. I lived in a smaller cottage rather than the dormitories with only three other students, who became my siblings, and it took us an embarrassingly long time to realise how important our foster-mothers and some of our teachers were because there's so little grandstanding and fawning within the temples. And the mage students, as opposed to the noble ones, gain a place purely on their own potential regardless of ability to pay so even the favoured apprentice of a great mage is likely to be no one of any importance politically.