[gburt]

My teams also assign code review "in addition" to the regular workload, but this is always in the context of an agile team effort: we get done what we get done [1]. A developer takes a story and works on it until it is solved (or splits it appropriately), then another developer (or a few) are expected to do review.

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[1] I might be measuring productivity with story points in the background, but there is no "scheduled workload," this is merely an averaging/planning exercise.

The (correct, IMO) managerial effort to improve individual productivity is much softer and more understanding than that and comes with the understanding that your output takes many forms. Some of my best developers directly complete almost zero stories in a sprint because their time is spent on code review, pair programming, direct assistance and architecture discussion.