Absolutely guaranteed college boy can join club (8)
I believe the answer is:
ironclad
'absolutely guaranteed college boy can join club' is the definition.
I can't judge whether this definition defines the answer.
'can join club' is the wordplay.
'can' becomes 'clad' (I can't justify this - if you can you should believe this answer much more).
'join' says to put letters next to each other.
'club' becomes 'iron' (type of golf club).
'clad' after 'iron' is 'IRONCLAD'.
Can you help me to learn more?
(Other definitions for ironclad that I've seen before include "Protected as by armour - say an alibi" , "Early armoured warship" , "Unassailable" , "Well protected, like armoured alibi" , "Inflexible" .)