By request, I've put together a video of It Ain't Necessarily So, a song from Gershwin's opera, Porgy and Bess. My understanding is that this is from the Easy Gershwin for Clarinet arr. Davies & Harris, which is currently a grade 4 ABRSM clarinet piece.
Sorry, it's a long video again because I got too carried away, so here's some chapters to help find your way.
0:00 Introduction
0:16 Play through
0:55 Thoughts on the time signature and triplets
3:34 Let's play those triplets
4:01 About subdivisions
5:50 Some figuring technique - C to A and back again
7:08 The Allegro giocoso section - subdivide those semi-quavers
7:39 Allegro giocoso - slowly
7:58 Getting the rhythms "perfect"
8:34 A note about accents
9:35 Some figuring technique - Bb to C
11:39 Some comments on tonguing speed
12:24 The semi-quaver, quaver, semi-quaver rhythm
13:47 Tempo I - comments about phrasing and shape
16:20 Lead into Bar 31, then some comments about Eb fingering, airflow (singing) and reed strength
17:31 Lead into Bar 31 (again) - comments about subdivision
18:40 Finishing off - the concluding phrase
20:38 Cut time and how it changes things
22:23 Adding some decorations (stretch goal)
25:16 Vibrator (stretch goal)
27:36 Outro