The double paradiddle is six notes — R L R L R R (with the natural alternating mirror L R L R L L). Compared to the single paradiddle, you add two more alternating singles before the closing double. The shape is four singles plus one double: that's the rule, and it's where most students slip.
Six notes per group fits naturally in 6/8: one rep per bar with straight 8th notes, beamed in the standard two-groups-of-three. The downbeat of each bar is the lead-hand single; the closing double straddles the second beamed group of the bar. Two bars (one R-led, one L-led) make a full cycle, after which both hands have led once.
Watch the same trap as the single paradiddle: the closing double tends to collapse under tempo. The first note of the double rides the rebound from the prior single, but the second is its own controlled stroke — both must speak. The 6/8 framing helps because each bar shows the rudiment as a single complete shape, not stretched across triplet brackets.
Exercises
Sticking: R L R L R R — four alternating singles, then one double. R-lead only here; both bars repeat the same shape so the right hand learns its job before the left has to take over. The accent sits on the lead R (the downbeat of each bar). Don't push tempo until both notes of the closing RR sound equal.
Now the lead alternates each bar. Bar 1: R L R L R R. Bar 2: L R L R L L. Notice how the closing RR of bar 1 hands the lead to L for bar 2 automatically — the rudiment is self-perpetuating. No accents yet; just chase clean sticking and equal volume on every note. The challenge here is the handover moment — the last note of bar 1 (R) into the first of bar 2 (L) — that's where most errors creep in.
Accent on the lead of each bar — note 1 of the six. One accent per bar, two per cycle. The five notes that follow each accent must stay quiet and even, including (especially) the closing double. If the second note of the RR or LL pops up to meet the accented downbeat that's coming next, you've started anticipating; back off the tempo and re-balance.
Now the accent moves to note 5 — the first stroke of the closing double. This shifts the felt pulse off the downbeat and exposes the truth about your double: if the second note of the pair (the unaccented R after R-accent, or unaccented L after L-accent) disappears under the spike of the accent, the double isn't balanced. Slow the tempo until both notes of the double speak equally with the accent intact.