Interleaved vs. Blocked Practice: The Contextual Interference Effect

Practice Schedule

Reps per skill 8

Practice pace 2.0 reps/s

Retention Test

Delay before recall test 7 days

Live Readouts

Reps completed

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Immediate accuracy

Discrimination index D

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Predicted retention

How it works

This is a simplified quantitative model of the contextual interference effect from educational psychology (Battig 1979; Shea & Morris 1979): practicing several skills in interleaved order (ABCABC…) feels harder and produces lower scores during training than blocked order (AAABBBCCC), yet interleaving usually produces better long-term retention and transfer.

Each rep of skill k adds to a short-term strength S_k, boosted when the same skill repeats consecutively (a priming/fluency bonus that inflates in-session performance during blocked runs):

gain = g0 · (1 + p · min(consecutive_same − 1, 5))
S_k += gain
Immediate accuracy: P_acq(k) = 1 − exp(−S_k / K)

Every time the schedule switches to a different skill, a global discrimination index D increases — this represents the extra retrieval effort and inter-skill contrast that comes from comparing skills against each other in memory:

D = switch_count / (total_reps − 1)      (0 = pure blocked, → 1 = fully interleaved)
tau_k = tau0 · (1 + β · D)                (memory persistence, in days)
Retention(k, delay) = P_acq(k) · exp(−delay / tau_k)

Because D stays near zero for blocked practice, its retention decays fast (small τ); because D climbs toward 1 for interleaved practice, its retention decays slowly (large τ). Drag the delay slider forward and watch the crossover: blocked usually starts ahead right after training, but interleaved catches up and overtakes it at longer delays — the classic "desirable difficulty" finding.

Blocked / Interleaved — choose the practice order, then resets the trial sequence.
Reps per skill — how many practice trials each of the 3 skills gets in total.
Practice pace — how fast auto-play advances through the trial sequence.
Start practice / Step ×1 — run all trials automatically, or advance one at a time.
Delay slider — simulated days between the end of practice and a recall test; recomputes retention instantly, no need to re-practice.

Skill A Skill B Skill C

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