Before you replace underperforming team members, diagnose the situation and take these steps to help them improve:

1. Review workload. Some potentially strong contributors can crumble if they feel overworked. Take stock of everyone's duties. Divvy up work so that no teammate faces an unfair burden.
2. Cross-train. Someone who struggles with one task may thrive in another job. Rotate assignments so that you give people a chance to surprise you by demonstrating a range of skills. Don't pigeonhole an employee because you assume he or she has just one narrow area of expertise. On a service team, for instance, switch members regularly from new-customer orientation to database management to survey design.
3. Pair up teammates. Ask an outstanding team member to mentor a poor performer for a few weeks. For example, pair a worker who lacks technical prowess with a high-tech wizard.
If disagreements erupt, remind everyone of the group's goal and the timetable for action. Strike a positive, forward-looking tone when teammates grow frustrated; don't let them engage in fault-finding and defensiveness. Tell the team, “Looking ahead, you need to…” instead of reviewing what's gone wrong so far.