Schoolfellow
/ˈskuːlfeləʊ/
Definition 1 of 1
Pro Tip 1/3Shared Experience
Use 'schoolfellow' to emphasize that you experienced school life together, more than just being in the same school. 
Our schoolfellow, Jane, will always remember the pranks we played together.
Pro Tip 2/3Impersonal Connection
'Schoolfellow' suggests a connection but does not necessarily imply a close friendship or current relationship. 
I ran into a schoolfellow from years ago, and we barely recognized each other.
Pro Tip 3/3Nostalgic Tone
'Schoolfellow' can evoke a sense of nostalgia when referring to people from one's past school days. 
Seeing my old schoolfellow brought back a flood of memories from our childhood.