Tartan skirt student included in garments (4)
I believe the answer is:
kilt
'tartan skirt' is the definition.
(kilt made of tartan material)
'student included in garments' is the wordplay.
'student' becomes 'l' (as in L-plates for learner drivers).
'included in' means one lot of letters goes inside another.
'garments' becomes 'kit' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'l' inserted inside 'kit' is 'KILT'.
Can you help me to learn more?
(Other definitions for kilt that I've seen before include "Under which, traditionally, a Scotsman wears nothing" , "Tartan clothing item" , "Tartan skirt worn in Scotland" , "Checked menswear" , "Bone; circle line" .)