The most common and most likely answer to this crossword clue is the 11 letter word AUDIOVISUAL
I've seen this crossword clue in The Sunday Telegraph
A
U
D
I
O
V
I
S
U
A
L
Buddy explains!

The straight part
We know that "Kind of teaching aid" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case kind of teaching aid = audiovisual.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does AUDIOVISUAL mean?
AUDIOVISUAL adjective- Containing both aural and visual elements.