yeah I think the question is how unique does OP want? - for him to be the only one in his class of 30 is certainly pretty reasonable, and not too hard to do stay out of the top 10 and you should be fine. Only one in his year group stay out of the top 100. Only one in his school probably stay out of the top 1000.
Slightly quirky fact is that there are many recognisable and easy to spell names that would still likely qualify as probably still rare enough to be the only one in their school like Colin Adrian Dougal and Isaac.
If you're aiming for "I've never seen that before" I'd recommend easy to guess pronunciation.
Possible suggests and examples of familiar / easy to read but still kind of unique:
Adam (#60) Adrian (#65) or Robert (#80) - likely the only one in his class, I think the OP is committed to the idea of something a little more unusual than this.
Jeremy (#231), Simon (#281), Martin (#301) Abraham (#319) Phillip (#606) Amos (#781) Alfred (#891) Devon (#884) or Dane (#927) he's likely the only one in his Primary school, and the only one in his school year once he hits Secondary, might well be the only one in his Secondary school.
Cedric (#1038) Allan (#1177) Elton (#1568) Harold (#1727), Caine (#1901) Barry (#1907) Roderick (#2168) Bradford (#2571) Alastair (#2602) and one of my favourites Eamon (#3169) Likely to be the only boy called this in his Secondary school.
Brennan (#1261) Bran (#6505) Cormac (#6635) Cavan (#6641) Archibald (#6691) Barack (#6699)Claude (#6712) Aiken (#9120) Selwyn (#11345) Colm (#12875) or Morton (#13688) Pretty likely to be the only one called this a person (even teachers) has ever met, well read people might recognise from fiction or history.