What you're training
Most progressions put a fresh root under every chord — the bass walks. A pedal point breaks that pattern: one bass note holds still while the harmony above it keeps moving, sometimes through chords the held note doesn't even belong to. This drill trains you to track the bass on its own line instead of folding it into "the chord," since a pedal is exactly the moment the bass stops describing the harmony.
Two levels, one skill
Level 1 asks the basic question: is the bass moving, or holding? Level 2 assumes you can already hear a pedal and asks which note is doing the holding — a tonic pedal (C, the expected anchor) or a dominant pedal (G, the tenser one that wants to resolve), with the exact same chords moving above it either way.
Go deeper
The bass that refuses to move — mined spans → shows how often real pieces reach for a held bass note instead of a walking one. The theory: prolongation → covers how a single harmony can be stretched across several chords, a pedal point's close cousin. Same bass-tracking ear, a different job for it → trains the same skill of listening to the bass on its own line, just when it's moving instead of holding still.
Where it fits
Comfortable with chord quality and chord inversions already? Pedal points is the next layer — the same bass-tracking ear, now listening for the moment it stops moving at all. The full drill ladder has everything else.