We analyze optimal task assignment when a firm needs to learn the abilities of employees. When projects require collaboration between juniors and seniors and only team outputs are observable, having juniors divide their time between two projects (“junior sharing”) is less informative about their abilities, but more informative about their senior teammates' abilities, than having juniors devote all their time to a single project (“no sharing”). In an overlapping-generations model, we show that no sharing is more (less) attractive than junior sharing if the prior uncertainty about abilities is small (large) relative to exogenous shocks to team production.